Personally, I doubt that the average person 'really' needs a full tower. A good mid-tower has more than enough room in it. I'll bet that the vast majority of folks that say they 'need' a full tower case really don't. What they are saying is that they 'WANT' one, and they are using the 'need' to justify going to the full tower.
But that's OK, as it all comes down to personal choice, and what you feel comfortable with.
I'm using the Cooler Master CM 690 mid-tower. I have 3 HDDS, a 3.5 floppy, a DVD burner, and Creative Front Audio panel in it and still have open bays.
Also, there is a good 2+ inch clearance from the end of my 3870 x2 to the HDD bays. So you can see that long vid cards aren't a problem with this case.
Now I couldn't have said that about the Centurian 5 that I upgraded from though, as my x1960 just barely fit in it, and there is no way in hell you could stuff a 3870 x2 in that rascal with out some modding.
With mid-tower cases and long vid cards, you will need to do your homework, and take a look at as many reviews as you can to see if they would have a space issue or not.