...Whatever you think of the relative merits of Heineken as a beer, you cannot disagree that it is not rare, exclusive, or hard to come by. ...
That's certainly true.
However, remember that in many people's view (but not mine), while its not particularly rare Heineken is
still very much perceived to be a 'high end' beer. Maybe it made it into the character's hand as a paid product placement (likely), or maybe it was just written in because it is familiar and by and large still viewed as a premium product (possibly).
The public at large has no idea what something like Westy 12 represents (and really doesn't care).
Personally I'd envision him sipping a Gale's Prize Old, from a large wine glass.