Your grocery store must have a terrible selection of beer. I home brew because I enjoy it. I'm under no delusions that my beers will ever be significantly better than the best I can buy in a store.
The idea that the hobbyist will in general produce a far better product than an industry of passionate experts is kind of ridiculous.
Hey, now; either my grocery store sucks, or I am/was a dang good home brewer.
Seriously; when it came out well (2/3 batches), the only thing that could compete with it was straight from the microbrewery tap. Never could make a decent lager, but for any kind of ale, it was great. I blame freshness, which is an under appreciated beer quality. Also, lack of the now popular practice of overhopping; almost everything in the store these days seems to be an IPA or overhopped porter.
Maybe the beer at your grocery store just isn't very fresh? The better grocery stores around me have a great selection of beer that seems about as fresh as what I make at home. Maybe the distribution chain is better here (Seattle). I've never noticed freshness as an issue at least.
As for making exactly what you want, that's totally valid. If your palette doesn't quite match what the breweries are producing (e.g. you want less hops) then yes, you can produce a better beer for you at home.
Berkeley isn't exactly the Sahara.
Now I'm wondering if it wasn't my pride fooling me, but I am pretty dang sure you can taste the difference between belhaven (which I think languishes on a cargo ship before it gets to my local bevmo) and a home brewed clone which tastes like a fresher/better version of the same thing.
My favorite quasi-invention: beer with a small serrano pepper added to each bottle. It didn't age well (it eventually turned into beery hot sauce), but it was delicious for the first few weeks.
The idea that the hobbyist will in general produce a far better product than an industry of passionate experts is kind of ridiculous.