The news was confirmed by Macminicolo
Confirmed: RAM in the new Mac mini is not user accessible. Hard drive can be replaced/upgraded, though not keeping warranty.
The site does report that it is possible to upgrade the hard drive on the new Mac Mini, however doing so will void your warranty.
On the other hand, the new Retina iMac comes with user-replaced RAM, so customers can upgrade the RAM on their device at a later date. The MacBook Air, MacBook Pro Retina, and entry-level iMac also have soldered RAM, meaning customers can't upgrade RAM at a later date.
Apple first announced the Mac Mini Thursday with a lower $499 price.