There are some variables that could make a tap not as good. Dirty lines to the keg and over/under carbonation, not stored at proper temp. But they'd be the exception not the rule.
Domestic beer kegs generally aren't pasteurized just filtered for bacteria and carbonated to various amounts.
Any foreign brewed beer keg is both pasteurized and filtered for transport, pretty much the same as the bottled.
Cask brews generally aren't pasteurized or have added carbonation beyond the naturally occurring.
(Learned from visiting a friend at Full Sail)
In the UK all kegs are pasteurized, filtered, etc. only casks aren't. (learned at Fullers brewery)