Personally I think using raw presets and sounds (keyword is raw, i.e. untweaked, unchanged) usually only gives a generic, even if slightly better, feel to your tracks. The sounds aren't yours, and depending on said sounds, are heard in plenty of other tracks, hence the generic feel. It often kills the track (at least for me), especially if the composition (both melodies and drumwork) is great.
It's important to focus on both sounds and composition. You can take it easy in either area if you're starting out and want to take smaller steps, but by the time your standards go up, you can't leave either one out, or else you'll either get a very boring but well-produced track, or a moving track that's a pain to listen to.
Rawmin - true enough. Thing is, in rock (I'm not a big rock listener so I might be wrong on this), it's often not what sounds you use, but how you use them - for example, there are plenty of different amps/amp settings and playing techniques for a guitar. This is my philosophy as well. My favorite (and only :P) VSTi I use is ReFX Nexus, which is entirely presets that often sound really generic due to being used time and again in multiple tracks. I don't use them raw, instead, I tweak them beyond recognition, layer them, or use them creatively - I've used synths out of the Bass section for leads, for example. ;D