Don't be a Celeron hater. 

  There may be reasons for the decision, such as bupkus needing the Celeron for testing purposes. ActiveX has a limited budget but wants a P4, presumably for performance reasons. Now, you can say that A64 would be a better choice, but how about this for an upgrade path for those with limited budgets...
SCENARIO: Has X amount of total cash for complete system. Allocated $80 or less for motherboard and CPU. What to get...
CHOICE #1: Socket A Sempron with motherboard. Upgrade path would be better motherboard to overclock socket A Sempron to something better or faster CPU on original motherboard with 333MHz FSB max, AXP 3000+ fastest "official" CPU on a non-overclocker board. Still stuck with socket A platform, not higher performance A64.
CHOICE #2: Socket 478 Deleron with motherboard. Upgrade path would be better motherboard to overclock Deleron to something better or faster CPU on original motherboard with 800MHz FSB max, P4 3.6C fastest "official" CPU on a non-overclocker board.
Oh well, whatever. I personally like all my budget processors, be they Deleron, AXP-M, P4A, Duron, whatever. Oh yeah, haven't actually laid hand on a Sempron yet, but if the 3100+ drops to $100...