I own a late 2011 MBP which according to Apple has a miximum memory capacity of 8GB (2x 4GB).
I installed 16GB (2x 8GB) which I purchased from Crucial.
So, I'm not certain of why Apple does what it does, but I was able to install 16GB with no problems so far...
That way Apple is able to get more people to "upgrade" to the more expensive models if they think a certain model won't handle the RAM they need. It's nothing but a marketing ploy to drive people to more expensive models.