More than anything, it changes our perception of the flavor. Certain subtleties are hidden by cold temperatures, as flavor and aroma uptake are subdued.
There are some other minor physical changes as well; given enough time, yeast will flocculate out a little bit more and CO2 will dissolve at a higher level, which IMO make the beer taste cleaner and crisper.
So yes, chilled beer is definitely different in taste, but I'd say more of that comes from our palates' perception than an actual change in the beer itself.