Simple answer is that some companies may offer discounts and so in order to get that discount you may either have to go through a particular affiliate or enter some code to get that savings to prevent everyone from getting that discount. So for example there are various "Dell deals" as they are known to get the price knocked down on a Dell. In some other cases it may be that you saw a refurbished laptop rather than a new laptop and thus as such it is going to be cheaper as the refurbished one is kind of like a used car. May still be good, may be a lemon. Who knows for sure.
Course in other cases you may be seeing places where someone offers mail-in rebate scams which can also happen in some cases I think.
Regards,
JB
Home Desktop: VoodooPC Hexx. AMD Athlon FX-60, 2 GB RAM, 2 x 250 GB HD, 7900 GTX video card.
Home Laptop: HP dv4000, Pentium M, 2 GB RAM, 80 GB HD, ATi 700 Radeon Mobility