H.264 Blu Ray will play in most players, H.264 will not. Is this true?

I was told that the H.264 is a universal format, but to make it play to Blu-Ray standards for players you must use H.264 Blu-ray.  If not, it may not play in all Blu- Ray type players . The same goes for MPEG-2 Vs. MPEG-2 DVD.

Is this true?

Thanks in advance

Premiere Pro CS 5.5

Encore 5.5

Media Encoder 5

Power Mac Intel Xeon

10GB RAM