A lot of gamers were questioning why it wasn't possible to access games in offline mode in Steam while an account was suspended or banned, but the real news is that you already can, Valve just never told anyone. What's more? Your games aren't limited to offline mode.
While Valve doesn't have a lot of legal lingo surrounding the use of their digital distribution service, they do make it known in the subscriber agreement consent form...
Valve may terminate your Account or a particular Subscription for any conduct or activity that Valve believes is illegal, constitutes a Cheat, or which otherwise negatively affects the enjoyment of Steam by other Subscribers.
One user put that clause to the test and was aptly banned, however, he later found out that he wasn't completely blocked out of accessing his games because of a recent policy update in Steam for account access, which has now been deemed as "account locking" instead of "account banning". According to a Steam volunteer moderator, he makes it clear that...
Steam support stopped disabling Steam accounts a bit more than two months ago. This has been replaced with "account locking": you still have access to your games, but some restrictions are applied to your account (no trading, no cd key activation, no purchase allowed, etc.).
He provides proof of this with screenshots of an account being banned but still having access to games in offline or online mode, which we were kind enough to let you view below just so you know that you're not having your junk pulled.
This means that gamers who have been banned either for fraudulent or nefarious purposes with the intent to use their Steam account for other activities other than gaming like an upstanding member of the interactive entertainment community, can still access the games they paid for. There are simply restrictions added to the account but the content you paid for is content you still have access to.
Valve actually offers quite a bit of leeway in using their service, so getting banned is not something that's particularly easy to do so long as you follow the rules. There are, however, some rare exceptions where tertiary license agreements are put into place for Steam games, particularly, EA's games on Steam, where an EA EULA for a [now absent] product on Steam basically outlines the same sort of restrictions you would find on Origin. Of course, since it's Steam, there's no worries about "losing entitlements" or having third-party software scan your PC for you.
Valve's head honcho, Gabe Newell, recently spoke out against these sort of practices that EA is using for Origin, saying that as the service stands right now it's just not up to par to where it should be for consumers and gamers, and it's justnot doing anything super-well at the moment. It's kind of hard to argue against that point.
At least gamers who went off the deep end and managed to get banned can still play their games and access the content on both Steam and Origin. So, in that regards, it's a win-win situation for gamers no matter which digital distribution service you use.
[Update: Steam's official support representative has stated that "Games registered to suspended accounts will no longer be accessible; even in offline mode." Of course, the support didn't clarify if this applies retroactively for suspended accounts or the distinction between a suspended account or a locked account, so we're awaiting official word from Valve on the matter.]