The answer is cultivated vs. wild.
I picked blueberries in Maine (West Kennebunk) the week of August 1st, and they were large berries. This means they are cultivated, meaning that at some point the farm(er)planted blueberry bushes as a crop.
The larger berries, often referred to as "nickel" sized, are almost always cultivated berries.
Wild bluberries most often tend to be smaller, hence the difference in flavor.
Many times blueberry patches are often the outgrowth of de-forestation or forest fires.
I remember as a kid in Nova Scotia and Maine going into wooded areas where my uncle had told me a forest fire had been through years before and finding blueberries among the scrub brush.
Wild blueberries are more readily available the further north you travel in Maine-Washington county especially.
As far as the Bluberry Ale is concerned, this is usually a wheat beer with the bluberries added to the mash. This is different than many brewpubs, like Boston Beer Works, which may pour real blueberries in syrup in the bottom of a glass, then pour wheat beer over it.
Many places don't brew it because they must clean the blueberry flavor out of the kettles afterward, and it is time consuming. Same reason many brewpubs or breweries do not make homemade root beers or sodas unless they have special tanks designated for just that.
What Paul had sounded like Bar Harbor Blueberry Ale from Atlantic Brewing Co. of Bar Harbor. This company started as a small batch brewery, and really made their reputation with this as a signature product among others. It really doesn't get distributed very far south, it is hard to find in Boston. 3 Dollar Dewey's in Portland usually has it on tap.
I have had 3 different samples this year so far-the aforementioned Bar Harbor Blueberry, Sea Dog Wild Blueberry (now owned by Shipyard Brewing), and Wachusett Brewing (berkshires,MA) Blueberry Ale.
CheeseWit, you can definitely find this beer at the Portland Public Market in downtown Portland. SeaDog Wild Blueberry Ale will be on sale in 6 packs in Kennebunkport (try any convienience store), as well as just having reopened brewpubs in the Rockland,Topham, Camden area.
While in Kennebunkport, I suggest a trip to Federal Jack's brewpub, owned by the Shipyard Brewing Co.. They will have raspberry wheat bear on tap, made the same way as the bluberry ale.
Downstairs is an artist who paints wonderful portraits of Civil War generals, as Shipyard Brewing is paying homage to 12 different generals on beer labels. Joshua Chamberlain has a beer named after him.
Sorry if I rambled folks, didn't mean to drag the topic from blueberries to beer.