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.
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.