I would use the term 'fluid' rather than 'fast'. 40K is very fluid and reactive in play style--you typically have many more (percieved) options on a unit-by-unit basis. That said, I find 40K to be oddly more predictable in outcome--there are fewer make-or-break rolls than there are in Fantasy, and I've found my fortunes far more likely to swing wildly from one side to the other in WHFB than in 40K.
Granted, you don't get shot off the board in Fantasy, but combat is frequently far more decisive and is engaged in more readily. I find 'whittling' to be more of a 40K thing, especially given the prevalence of cover, stubborn, and ridiculously high leadership scores.
As for 'more accessible', I can't really comment. I haven't found one to be more accessible than the other, precisely (and I don't ascribe to the view that one or the other is more 'tactical'), though I will readily concede that the number of rules makes the learning curve in Fantasy a bit steeper. If by 'accessible' you mean 'easy to pick up and play quickly', I agree with you. If by 'accessible' you mean 'easy to become interested in', I don't think that's necessarily true.