Dubstep's characterized by the off-beat drums and shit I think. I am pretty sure that is the main defining factor, look at the wiki page.
I'd like to expand a bit. Dubstep is a fusion between the Breakbeat/Drum and Bass style breaks, mixed with Dub, and Grime, all rolled into one. Of course, there are varying influences in individual artists and such, but that's the summery of it's main influences. It doesn't need to have offbeat drums, there's lots of it out there that has basic 4/4 beats.
The original Dub genre, where Dubstep gets it's name, happens to be a sorta subgenre of reggae. It bares almost no resemblance to reggae any more, though. It's basically the riddim from reggae tracks that has been remixed and such, emphasizing the drums and bass. Basically, the more laid back and empty sounding dubstep that lacks wobble bass sounds a lot like Dub.
The influences from Drum and Bass and Grime are what give Dubstep it's offbeat drums (DnB), dark sound (DnB) and crazy basses (Grime, well, sorta).
Example tracks:
Dub:
Grime:
I dunno how representative this track is, because I know very little about grime. If it helps, Dizzee Rascal is also grime.
Dubstep Example 1 (no wobble bass!):
This track is really laid back, has no real crazy bass, but is still considered dubstep.
Dubstep Example 2: (crazy fucking bass):
This is probably one of my favourite dubstep tracks of all time. It does have wobble bass, but uses it in a really unique way, and mixes it with some really high end synth.