These are the kinds of little incremental pre-Epic price creeps we were talking about in the Kong thread. They need to tighten the budget this year, and that means little tweaks to keep as much money circulating back to them as they can.
It's certainly not fun to see these kinds of things, but I'll be completely honest that I get Butterbeer so infrequently that an extra .50 cents for a cup is not something I or many, many other people will even blink twice at. On the scale of Rollercoaster Tycoon-style MinMaxxing, this is incredibly tame.
Now if they pull a harsher move and bump it up to $10, or god forbid $15 for the same cup, then that's something to really cause a stir about. Simply no good reason for that big of a bump at all.