One of the things that has been tossed back and forth between fans of PCs and Macs for years is that the PC platform as a whole is much more open and upgradable than the Mac world. You can upgrade minor things on most Mac notebooks and computers like the hard drive and RAM generally. In fact, it's fairly common for many buyers of new Mac computers on a budget to buy the machines with the base amount of RAM and storage and then upgrade it aftermarket parts. Those aftermarket parts are often cheaper than buying the computer from Apple with the upgrades installed out of the box.
iMac upgrade purveyor OWC has posted up a blog that talks about the new iMac computers and how much more restricted upgrades are on these machines than the older version of the iMac. Apparently, HDD upgrades were easy with older version on the iMac, even if the fans did sometimes spin out of control and annoy users after upgrading. Since late 2009, you could upgrade the HDD inside your iMac with another drive of the same brand, and things were fine since the special thermal sensor cables would still work with the same brand of storage drive according to OWC.
The problem with the new iMac line that launched recently is that Apple has vacated the standard realm of cabling and gone from the normal 4-pin power cable coming to SATA drives and moved to a 7-pin cable. The reason for the cable changes is apparently to regulate the temperature inside the machine using the larger cable in conjunction with custom Apple firmware on the HDD. OWC reports that removing the new iMac HDD from the machine will cause the fans to spin at full speed and the replacement of the HDD with anything not Apple original will result in the iMac failing the Apple Hardware Test. This all means that upgrades to the internal main 3.5-inch HDD inside the new iMac won't happen, at least for now. Do you think this is Apple's way of forcing people to buy its hardware or is this simply how Apple is dealing with heat management?