HP does not support 64 bit Solaris 10 on INTEL Xeon

Look at this Solaris 10 support matrix for HP's servers, you can see the BL25P, BL35P, BL45P, DL145, DL385, Dl585 servers support both 64 bit and 32 bit Solaris 10. The HP DL140, DL360, DL380, DL580, ML370, ML530, ML570 only support 32 bit Solaris 10.

Now the quiz: what is the difference between these two groups, why is one group 32 bit only?

Hint: the model numbers of one group end with 5, indicating they use powerful 64 bit processor, the other group's model numbers end with 0.

Hint: It seems one processor vendor is enjoying 100% of the 64 bit Solaris 10 x64 market.