Why Biostar NF325-A7 support faster Athlon than Sempron?

The following was previously posted as "Question for Paul":

I purchased a Biostar NF325-A7. On this page:
http://www.biostar-usa.com/cpusupport754.asp#NF325-A7
It specifies support for Athlon 64 up to 3700+ and Sempron up to 3100+.

Why does this MB support faster speed Athlon than Sempron? Would you say the
Athlon 64 is a better choice than Sempron or Sempron 64? If so which speed
Athlon 64 is better than Sempron or Sempron 64? Is speed rating a deciding
factor? In other words is Athlon 3100+ as fast as Sempron 3100+ or is Athlon
inherently better regardless of speed?

I have already purchased a Sempron 64 3100+ so these questions are to
satisfy my curiosity however I have l since located an Athlon 64 3200+ and
may buy it too.

I just now noticed that the above page doesn't say anything about Sempron
64, just Sempron. I bought a Sempron 64 3100+. I hope it works with my MB.
Do you think it will work? Sorry if this post is confusing. I'm starting to
get confused!
Thanks
pcbuilder98