Alright, first of all...
In any Diatonic Major key there is only One dominant chord. That is the five chord - or V7 in traditional nomanclature.
Dreamword is using the dominant 7 as every seventh chord, instead of appopriately alternating between the seventh chords listed above by Eliah.
Instead of using the dominant 7 everywhere you want a 7th chord, use the major 7, or minor 7, appropriately. Like this:
Cmaj7 Emin7 Fmaj7 Dmin7 G7 Cmaj7
Dreamword seems to be confusing the use of seventh chords in ordinary songs with the use of sevenths in the Blues form. in the Blues, all chords are dominant 7ths, even though this makes it not a diatonic key. Also, funk often uses dominant 7ths exclusively, but that is a much looser rule.
It's understandable, tho... Most cats will call a "Dominant Seventh" chord simply a "Seven" chord for short.
Using seventh chords can add a deepness to your music that typical triads cannot. Minor chords can sound darker, major chords can sound brighter... then throw in inversions, and you'll get minor chords that Sound major, and other such wacky oddities.
Memorize what chords are diatonic in each key, and you'll learn to substitute regular triads with the appropriate diatonic seventh chord with much less thought. Its not as easy as lowering the root a whole step, but it is not impossible. It is fundamental to any jazz player, or any well educated all-around musician.
So get it right, goddammit... just kidding... goodluck.