This. PC vendors generally assemble parts made by other people. By and large, their trackpads can only as good as the best one available from third party vendors. Since PC vendors just assemble parts, it creates a race to the bottom scenario because that's the only way they can really differentiate an amalgamation of commodity parts. Also, PC's are usually sold on spec and it's difficult to quantify how good a trackpad works.

Since Apple designs their own stuff, they aren't reliant on other people to make a good trackpad, and they charge a premium for it.