This is really not that difficult, or it shouldn't be. 4e is D&D, same as all the other editions. It doesn't matter what some people might say, because it won't change the reality of the situation even a little bit.
Let's try an example from a different angle:
This is a 1961 Chevrolet Impala SS.
This is a 2006 Chevrolet Impala SS.
They're completely different vehicles, not only superficially, but also fundamentally. The only fundamental things they really have in common is that they were both produced by the same company and feature internal combustion engines that run on gasoline as their means of propulsion.
But they're both Impalas. Nothing in the world will change that no matter how much different they look or feel.
EDIT: And because of people's heightened sensitivities these days, I guess I have to mention that I'm not trying to compare any older edition to a clunky old boat of a car, nor am I trying to compare 4e to a sleek new vehicle. Conversely, neither am I trying to compare an old edition to a classic vehicle and 4e to an unimaginative, cookie-cutter conveyance that looks like all the other cars on the road.
And it's pathetic, frankly, that I need to add that disclaimer, but without it, I know full well I'd be accused of any and all of what I just mentioned.