Cost is another big factor! Macs are more expensive, the software is also a lot more expensive compare to PCs.
I have had a IBM laptop for a past 3 yrs with windows xp and I am very happy with it. When I bought it, it was a top of the line computer and is still serving me well (with mac, I bought one ever year

I do have access to considerable discount for Lenovo (formally IBM) PCs, if you are interested, pm me and I'll provide you more info.