Re "mass market" beer --
The provided link discusses retail sales of beer (i.e. convenience, grocery, & liquor stores) but not beer sold at bars. I'm guessing including that would bump Sam Adams up a notch... I personally don't tend to buy plain-old Sam Adams to drink at home, but it is often the only decent thing on draft at many bars and restaurants. And FWIW,
this link says Sam is the 5th largest US brewery while Sierra Nevada is the 7th largest. I think the distinction for me is really just the fact that Sam Adams has TV ads and Sierra Nevada doesn't (where I live anyway) -- that's what makes it "mass market" to me, at least. Either way though, I enjoy the beers produced by both companies

I'll be on the lookout for Sierra Nevada Celebration, I haven't sampled that yet.
I'm sad and wistful now, thinking about how I miss Bell's White Winter Ale and wishing that it could be sold in Illinois...