Yes. Most believe this to be the case.
Some have gotten good results with a projector.
I can get decent results on my DLP with some systems, particularly the oldest (Atari 2600, Colecovision). I get terrible results with systems in the middle...Nintendo, Master System, SNES, Genesis, and the Nintendo 64 is the worst. A device called the XRGB can reputedly make dramatic improvements, but I have not been will ing to cough up a $200 for it.

A new technology called SED (or OLED) looks hopeful for future sets. It is supposed to combine the both of bothe worlds, that is, CRT + LCD or DLP.

You can use one of the many plug-n-play games to get an idea what sort of results you might see from the older systems.