Ignore for a second the fact that beauty can't really be quantified into a definitive list. Ignore for a fact that if everyone who reads People made their own list, it would probably be radically different than the canonical yearly list. Ignore the fact that when People's online poll for the same list was dominated by someone known as Hank, The Angry, Drunken Dwarf.
Simple logic destroys this list. Ali Landry was on the list in 1998. Since that time, she hasn't changed much in any way, shape or form. Yet she wasn't on the list in 1999 and 2000. I wonder why? Logically, there's only one reason why - there's now someone more beautiful. But who? Well, there's a fifty-something year old woman on the list for the first time this year. So maybe it's her. But, unless she's undergone some massive changes herself, she hasn't changed much in the same span of time. Wouldn't it stand to reason that either (a) Ali Landry is still better looking, or (b) Ali Landry was never better looking. Either way, the list is wrong. And that's just one instance. There are at least 25 each year. Because People chooses whoever the hell they want. Got a hot movie coming out? You're in. Cause any controversy lately? You're in. Seen cavorting with Leonardo DiCaprio on the beaches in France? You're in.
In reality, the list should be titled: "People's 50 Most Beautiful People Who Are Currently Trendy To Talk About And Have Done Something Recently Which We Can Write A Few Paragraphs About". But somehow that's just not as catchy.
As a late addendum... I agree with theonomist on the theoretical aspects of beauty. But let's not kid ourselves... this is People Magazine.