It’s simply another Intel architechture. Just as the 386, 486, Pentium (which had two socket designs), Pentium Pro, Pentium II, Celeron (available in socket and slot designs), Pentium III (also socket and slot designs) had different interfaces.
Actually, the Ghz Pentiums are the first new Intel core (true 7th generation) since the Pentium Pro. Plus (I may be mistaken here) I think that the only motherboards available for the Willamette (Pentium IV) core are going to require RAMBUS memory. Which you would only find on motherboards made in the past 6-8 months or so.
If you want more technical info, I’m sure I could dig up some links for you.