Yeah, just like releasing a shooter with broken bullets or a football sim without a ball - totally not an issue, you can still run around and do stuff, right?
That's not exactly the same comparison, dont you think? It's more akin to a shooter game where you dont get any new weapon/rewards after you finish a level, or a football sim where you did not win the cup even if you placed first.
Either way, the mechanics for the game (combat, quest handling) is not broken, just the xp award that is bugged at the moment. If you're that bothered, you can always install the temporary workaround mods to continue playing (just remember that grayed quests give no xp so if you install the one that still gives XP, then you can also consider yourself cheating at this game, but its SP so who cares).
Personally, i think that this is not a game breaking issue, but it is a pretty severe bug (since not 100% of the playerbase experienced this).