Have a look at your screen.
Have a look at what that cheapest 27" monitor costs. - don't get started with $300 HDTVs with a resolution of 1920x1080, these are 2560x1440.
Add that on top, substract your old screen and you have a difference of US$450 on the 27" same-spec'd i5 iMac. These things are - like a laptop - manufactured at Foxconn, don't forget that. Your i5 PC is hand-made out of parts which came out of a machine and put in a carton. So in the end this is the same $350 difference as it is with the laptop. On custom PCs however, you don't really have something like AppleCare.
And the 21.5" iMacs are overpriced, no doubt. But they are due to be updated, probably Tuesday. Let's have a look again later.
It seems more and more that it's a myth of the overpriced Apple products, based on misunderstanding of the product line, the update interval and the reading of raw specs, in which they superate the mainstream PCs. All I can see is a general +$350, which gets subtracted to +$250 on the first major update, and is ±$0 if you put the stuff on eBay when you're done with it. The line-up is not bad. However when you look at any one year old Mac on the Apple Store, whose price hasn't been corrected to the fluctuation on the market, with hardware prices dropping each day, that just gets misunderstood.