Kamikaze Midget said:
"Making it up as you go" does not correlate directly with "Don't have a baseline."
D&D has a baseline. That doesn't stop me from taking that baseline and beating the ever-loving snot out of it every time I jump into the DM's chair. And it's much, much, much more fun to know how badly I'm beating it than to just keep punching and wonder if it's dead.
This statement, I think, is the crux of the matter.
Even with all the rules in place, and D&D/d20 being more balanced now than it ever has been, there are still aspects of the rules, ideas and core-cows that my friends and I are always either going to disagree on, or grind up into sacred burgers. This happens with every system.
The "baseline" of an RPG is merely your starting point. Eventually, even among the players and GMs who always use the rules-light approach, you will run into a snag in any system you play in for any length of time.
I have never liked the system for any of the Palladium stuff. It's too obscure and top-heavy if played as written. I love the concepts of Rifts, though. I just bought all but one---they didn't have it, at the time---of the supers books because the powers are so cool, to me.
On the other end is D&D as it stands. As much as I like the streamlining and rather easy workability of the 3e+ rules, there's really not enough flavor there, and in many cases, it's because of the streamlining.
It seems that all RPGs have a little something to offer. Even if it's just one idea or rule-modification, that's still something. To boil them all---or even two of them---together pre-sale would take away alot of the fun.