Not exactly. First of all, you have 1 drive instead of 2 which means fewer platters, cooler operation, less noise among other things. Secondly, the WD Green drives are mostly used as storage and media drives which are not written to/read from on a daily basis. There are plenty of reasons to get the 1TB over 2 x 640GB, the primary of which are QUIETER operation, COOLER temperatures, and LESS power consumption.
All valid points but.... you're pickier than I am