Hell, I probably buy MORE beer since I started homebrewing. There's tons of styles to try many of them I am only now reaching out and trying, and different commercial examples within each style.
And I will usually try several version of a style, especially if I am interested in coming up with my own recipe.
I make great beer, and some of it would stack up against many commercial beers. In fact in a taste test my rogue dead guy clone was like better than the original, and my bell's amber clone is a pretty dead on to the original. But there are many beers I like that I will prpbably never get around to brewing-style maybe, but not a specific clone of it...Like I will probably never be able to make an Oaked Arrogant Bastard clone that will be as perfect as that is...I may make a great beer like it, but I doubt I will ever make it exactly.
But I like so many different types of beer, that even if I may have 3-9 different types of homebrew on hand at any given time, that doesn't mean I suddenly won't have a craving for something specific on the way home. I did that this week, my wit is still in the fermenter so I picked some hoegaarden on the way home. Or like I said an OAB....
I know a lot of brewer's never buy another commercial beer...but me personally, that would be like cutting off an appendage, and severely limit my enjoyment of the whole beer culture thing that I am so geeky into.