Chill out n00bstar, there is some truth to UncleBibby's words...
This is coming from someone who absolutely loves analyzing music, it's fun and can teach you a lot about how music is structured--but comparing music theory to the laws of gravity is a bit of a stretch. You'll find that music theory doesn't really analyze Eastern music well at all; a lot of it deals with very subtle modal stuff that the West mostly ditched with TET. And it's barely catching up with poly-rhythms, something Africans have known about for centuries and centuries. Not to mention the 20th century composers such as Debussy, Scriabin, Ravel, etc., strict theory tells us that stuff really shouldn't work... but it works, exceptionally so. And there's no real way to build compositions like theirs from scratch using theory.
I've said it before elsewhere, but I think of music theory as mostly a reverse-engineering of successful techniques in revered compositions. But every single trailblazing composer has been called a lunatic and a heretic by his era's music theory. So writing stuff that makes you feel good could in fact create something that couldn't be arrived at with theory. Just something to mull over. My personal credo is write first, ask questions later (optional). On the other hand that doesn't mean theory's worthless, and you can learn a lot via analysis... Don't mind me, just playing the part of both devils here
More on topic, I didn't see it posted but it's extremely common in blues-rock to substitute a bVII chord as a surrogate V; plagal cadences are used a lot too. And I can't believe no-one's mentioned tritone substitutions yet. Those can be really fun! Blues is especially tricky though, most experienced bluesmen will sing and play notes between the twelve-tone western set (Robert Johnson is a master of this), making the search for an all-inclusive scale sorta pointless.
Though, jumping off from that, I find that melodies can absolutely bend harmony to their will. They're delicate and can be imprisoned by a premeditated turnaround (it's why I'm wary of writing progressions first), but you can lead from any chord to any other and it will work--with the right melody. To say nothing of using a walking bass-line or slash chords to connect harmonies tighter (which is still a kind of melody). Melody is king, pretty much.
Fun topic. I agree with the others who said this, there needs to be more discussions on topics of this flavor.