It's wrong to compare iMac to a desktop PC. Apple uses laptop components inside the iMac lineup. Not only in the CPU, chipset, GPU but also the optical drive. Only exception is the HDD. So, any comparison with the desktop components is wrong. There is a performance hit due to use of mobile components, but on the bright side it brings power efficiency to the PC.
For those unaware, cafegadgets has good deals on the new iMac lineup. The entry level iMac (new one) series starts at around 61k.
*www.cafegadgets.com/iMac
Those who think of buying (not craving for) an iMac (atleast in India) wouldn't care what the desktops have on offer.