Because the Celeron has always been seen as the copycpu from the pentium. if you compare the celeron with the pentium that comes from the same year, the pentium is your best bet.
in this case. the celeron has been launch 6 month later than the pentium.
you dont have to worry which one you pick between the 2.
for how the market stands. pick the cpu that does the least harm to your wallet
so if you see an celeron for $10 and an pentium for $5, take the pentium.
also avoid ebay. lot's of cpu scam's