iFixit has a teardown of Apple's new Mac mini. The device is impossible for normal users to open up, only the HDD is user replaceable, but after you disassemble the Mac mini completely and all other parts are soldered down or proprietary.
The only reason I can see Apple lowering the Mac mini's processing power and removing user access to RAM is them planning on releasing an ARM based model in the near future with a logic bord similar to current iPads. A low powered machine than uses even less energy than the current Mac mini's useable as a server or media center. But aside from this strategic approach, I can't see why they take options away.
When they killed the Xserve, they pushed the Mac Pro Server and Mac mini server as good replacements. With last years Mac Pro release, only the mini was a good choice when building a server. Now... It's a pity they harmed this little machine so much. The Mac mini was a robust and powerful (home) server. Now it's an expensive low end device without any future.