Anyway, when ordering in a restaurant, should there be any expectation of serving size when ordering a beer (assuming none is listed)? My personal assumption is a 20* oz Imperial pint, but I usually dont get that.

Should I assume an American Pint? Because that is pretty rare too. The only thing worse than no size being listed, is when pint is listed and then you get served in a standard shaker "pint" glass, that holds 14 oz if lucky (or unlucky, because they hold a 12 oz bottle + head, so you are getting a headless pour if they fit 14 in there). The first is sort of buyer beware, but the latter is fraud.
*I realize that an imperial pint is 20 imperial ounces, which is only about 19.8 american ounces.