Not really
I'd miss Ars Magica, Paranoia, Over the Edge and Call of Cthlhu right off the bat. I'd argue that none of these games could be converted to d20 and still maintain the right feel. Paranoia and Over the Edge especially - they're too loose and too "make stuff up as you go along" to really mesh well with the d20 mindset. There was a d20 CoC conversion (a very good one, actually) but it gives a different flavor to CoC than the BRP system does - d20 doesn't model lack of competence very well (this is probably why I don't think Paranoia would fit either - d20 characters are measured by what they're good at. Paranoia characters are mostly measured by what they suck at). And while Ars Magica might be rightly seen as "proto-d20" in a lot of ways, the use of a d10 versus a d20 makes a huge difference in the scaling of the game (as anyone who has tried to do a conversion of the spellcasting system to D&D might recognize).
d20 is a great system for running games that conform to d20 assumptions. And I don't mean things like "Vancian magic" or "hit points" or "armor class", but instead things like "characters will generally be competent in combat" or "random luck should count as heavily as competence in conflict resolution" or "character skills should progress at roughly the same rate for a character as he gains experience". Arguably, most RPGs are built with many of these assumptions anyway, and using a well-constructed d20 variant for them is likely a good a way to go as any. But its nice to have alternatives systems out there for games that don't fit with those assumptions.
I'd miss Ars Magica, Paranoia, Over the Edge and Call of Cthlhu right off the bat. I'd argue that none of these games could be converted to d20 and still maintain the right feel. Paranoia and Over the Edge especially - they're too loose and too "make stuff up as you go along" to really mesh well with the d20 mindset. There was a d20 CoC conversion (a very good one, actually) but it gives a different flavor to CoC than the BRP system does - d20 doesn't model lack of competence very well (this is probably why I don't think Paranoia would fit either - d20 characters are measured by what they're good at. Paranoia characters are mostly measured by what they suck at). And while Ars Magica might be rightly seen as "proto-d20" in a lot of ways, the use of a d10 versus a d20 makes a huge difference in the scaling of the game (as anyone who has tried to do a conversion of the spellcasting system to D&D might recognize).
d20 is a great system for running games that conform to d20 assumptions. And I don't mean things like "Vancian magic" or "hit points" or "armor class", but instead things like "characters will generally be competent in combat" or "random luck should count as heavily as competence in conflict resolution" or "character skills should progress at roughly the same rate for a character as he gains experience". Arguably, most RPGs are built with many of these assumptions anyway, and using a well-constructed d20 variant for them is likely a good a way to go as any. But its nice to have alternatives systems out there for games that don't fit with those assumptions.
