I agree with your analysis that people who have done striking arts usually "plant" much better when attacking than "Aikido only" types. An exception to this is people who have done heavily sparring oriented styles that emphasize speed to the complete detriment of power. They don't root much into anything.
Interestingly, I find this dichotomy within myself, and it's kind of amusing. In my old style, where striking was considered a vital skill, we attacked almost exclusively with what are usually called "reverse" punches, where the attacking hand is on the opposite side of the leading leg. In Aikido, we attack almost exclusively with the same arm as the forward leg. When I reverse punch, I plant pretty darn well. With an Aikido punch, I'm much lighter and easier to throw.
I also wonder why neither of my styles "mixed it up", and taught throws for both kinds of attacks, since it changes the relation between the attacking arm and the "3rd point" that we usually throw towards. While the principles should remain the same, a little practice would be helpful... *shrug* Perhaps I'll figure it out one of these years.