Firstly lets clear up the UK HipHop vs Grime. Hip Hop is at 80-90 bpm usually (correct?), grime is 140bpm. I'm not gonna lie here, a LOT of grime is pureeeeeeeeeeeeeeeeeeeee bullshit, but there is some good grime out there.
UKHH emcees do not use a fake american accent, if they do they look like idiots over here.
a few examples of UKHH
http://www.youtube.com/watch?v=m3cI-4RGfZM
http://www.youtube.com/watch?v=lDGJd1LwQ64
Heres a few examples of Grime which I think is pretty good
http://www.youtube.com/watch?v=lDGJd1LwQ64
http://www.youtube.com/watch?v=n2VFF4_tto0
Some old grime which have some beats which are similar to dubstep with those grimey baselines.
http://www.youtube.com/watch?v=TbghsfAlIq0
You can clearly see the difference between hiphop and grime. Grime emceeing is probably way more influenced from dancehall emcees than hiphop emcees. However some grime emcees can swap over and shit, which often happens when they get bigger (see dizzee, see kano).
Secondly, Dubstep
clearly has a large influence from grime music, espcially the older beats. When grime beats are made tho, they are made with the emcees in mind, so there is more 'room' left for them, where as dubstep, a lot more can be put in if u get what i mean. We all know Dubstep has a lot of influences grime is just one of them, so there is no point bickering. But because dubstep and grime beats do sound similar somtimes and are at the same bpm, grime emcees can emcee over them. Flow dan was in a grime group called roll deep. Newham generals often emcee at dubstep nights.
Thirdly, to you Americans making snide comments at the UK, you know what your doing. What's the point in those snide comments?
Myself I am white and middleclass. But a large majority of this country do live in poverty and crime ridden areas filled with gangs, guns drugs and all the other bullshit u get in American cities, and most cities round the world for that matter, and many people get killed. I'm sure if I was from Kingston/Jamaica (where somone is kileld every 6 hours) I could say "lol @ black people and guns in the US". There is a world outside outside the USA, just so you know, just because your corrupt government, your news channels, the majority of your celebrities and the majority of your population are ignorant dickheads, doesn't mean you need to be too.
And fourthly, why not ask Plastician lol?