Maybe another case of programmed obsolescence. Also, windows has a shit ton of stupid performance problems, and like 80% of them are related to the file system (fragmentation, "cacheing", stupid apis, &c). Just try to move a real big file in ms win to another directory. It is going to take ages.
Basically, crappy user programs * stupid ms windows * lots of useless shit shipped by default with the computers = lots of unnecesary work needed to be done by the computer in order to get basic functionality, giving the false sensation of the computer "ageing".