Rather than non-upgradeable a better term to use might be non-replaceable. I've changed out the battery and hard drive due to wear or failure in pretty much every machine I've had and that isn't possible with this one, and I can't say i'm hot on the idea of losing my machine for a few days for replacement (nor can I even afford to with work and school).
That's a personal choice though, I can certainly see the arguments for it as well.
That is why I get AppleCare. Got it on the old design as well. But the main things that would be upgradeable for the RMBP are already upgraded past what most people will ever need.