A response to some points made above:
1. Certainly profit drives the commercial music industry - but what is profit if not a measure of efficient allocation of supply to demand? To put it another way, commercial music would not exist without 10,000,000 people who want to listen to Britney Spears, and who are we to say they shouldn't?
2. I would cautiously suggest that the underground music scene is also guilty of making judgements that are not based on the merit of the music - usually in a negative way. How many times have you heard people equate success with selling out without really considering the quality of the music in question?
3. Two words: the Internet. You have total freedom (at least until transferring data is made illegal to listen to anything you want, commercial homogeneous crap or hardcore elite underground.
4. Nick Cave is commercial. They Might Be Giants are commercial. Tom Waits is commercial. Last time any of them toured my town the tickets were way more expensive than the cost of an underground gig. All of the people you list sell their music for profit. Furthermore, bands like Nine Inch Nails and Rage Against the Machine could hardly be said to have lost control of their art, but they are surely sold in the same stores as Christina and Mandy Moore.
5. This is another argument that is always wheeled out to defend underground music. I say to you: David Bowie was an instant smash. Led Zeppelin was an instant smash. Nirvana was an instant smash. Bob Dylan was an instant smash. Many, many great bands have recorded only one or two albums and then disappeared. If an artist is really, really talented then why should they toil for years in obscurity before making it big? It's like saying Michelangelo should prove himself with crayolas for a few years before we give him a paintbrush. Furthermore, if you care about the music itself as indicated in (2) then what does it matter to you who created the music and how long they suffered for?
6. If people like listening to it, then it doesn't matter what sentiments are expressed in music. Just because a lot of recording artists choose to target their music at the 'ooh I love you' market doesn't mean that they couldn't write about something else if they wanted to. Furthermore, I would point you towards the blues as an example of great, timeless music that basically all takes the form of either 'my woman done me wrong' or 'lord have mercy on me.' Lyrical content does not necessarily define music.
7. You have thus far praised a number of electronic artists and then have the gall to turn around and criticise the production of commercial music? Many underground bands don't even have instruments! And good production can turn a good record into a great record. A band like Massive Attack can use huge amounts of production as their most potent musical device to produce brilliance.
8. In my experience the types of bands cited as underground are typically in the same price range as the most commercial crap around. Spearhead recently toured my town and charged about the same price as Take That on their last tour. Bob Dylan was over $100. The only really cheap tickets are for bands that are basically from the local scene, which means that no-one international is ever that cheap. So, either you have to pay a bit more and see a much wider range of music, or pay $5 to go to the local punk pit and enjoy your rebellious freedom whilst clutching at your bleeding ears.
Do not, however, mistake these for the words of some teenage, top 50, radio single-happy, boy band loving son of a gun. I love good music - many of the bands cited above are in my record collection. What I can't abide is when people hate something because it is successful, and music is an arena where this attitude flourishes. Many people who are into cult bands and the 'underground' scene seem to be motivated by a desire to be better than all of the mindless sheep who listen to commercial radio. It is all to easy to spew bile at anyone who actually likes the plastic sounds of the singles chart. If people like listening to that music, who are we to abuse them? If people of lower intelligence want to listen to the same song sung by different teen icons again and again then how does that hurt you? Presumably you don't resent their commercial success because they are stealing the limelight, otherwise you would be wanting the music you love to become the music you hate. I love the Smashing Pumpkins, and nothing pisses me off more than people who like to demonstrate how 'down' they are with the band by naming Gish as their favourite album and Mellon Collie and the Infinite Sadness as their least favourite. It's like saying "I don't give a fuck about the music, so long as people I hate don't like it."
In the end, all music will be judged on its merits. 50 years ago Buddy Holly was the equivalent of Britney Spears, The Animals were the Robbie Williams of the early 1960s, but today we recognise the musical importance of their work with the wisdom of hindsight.
One final point: some music is not commercial for the simple reason that... it SUCKS! There is a fine, fine line between underground, edgy musical genius and a bunch of fools with guitars recording bad punk covers.