Most DRM systems employed by publishers still allow you to play your games regardless of the region you're in. The fact that Valve implemented IP blocking in their DRM which they market to 3rd party publishers is certainly every thing to do with Valve. Publishers couldn't use it, if Valve hadn't made it possible. Before then, all regional restrictions were separate from the DRM and affected point of purchase only. Now however, they can directly affect you based on your geographical region, and not region in which the purchase was (or was not) possible.
Further to this, it's not always the publisher who imposes the restriction, but Valve themselves -- such examples include Dragon Age: origins (which was temporarily blocked from decrypting in Japan -- so those who pre-ordered it in the US then moved to Japan were left with nothing until after the game was released in the UK). Another example is Red Faction: Guerrilla, which the publishers had slated for a worldwide release on September 18th. Valve didn't release it in Japan until December 25th.
While neither of those were SteamWorks protected, they both suffered from IP block imposed by Valve until the point of release. Modern Warfare 2 and the Total War Series though, do use SteamWorks IP blocking and remain blocked even once the games are fully released in all available regions. The only way to play those in Japan is to activate them from a non-Japanese IP address.
Now given how Valve have artificially delayed the release of not only RF:G but also Operation Flashpoint: Dragon Rising over here, despite both publishers insisting that such delays were not at their requests (and yes, I confirmed this with publishers myself), I have no trust in Valve not arbitrarily imposing limits on games at their own whims.
This is why I now prefer to pre-order/purchase games at non-sale prices from distributors which are reliable when it comes to releasing games. As I've said before though, as pretty much all available distributors in Japan are now boycotting SteamWorks protected games, there is no viable alternative than to purchase through a Valve. And would you really want to give (a large amount of) your money to a company you no longer trust?
Also apparently, the only other DRM that is known to actively IP block regions, is the rebranded Starforce DRM.

Unfortunately this is incorrect. As evidenced by Einstein's Theory of Derm, the integer "Steamworks" always negates any preceeding or even proceeded integer, in this case "Worms" which is a positive integer. However, by adding the Steamworks integer to Worms we end up with a negative integer, in this case "Bollocks".
Therefore:
Worms + Steamworks = Bollocks
If you require further evidence, try adding Steamworks to "Dawn of War":
Dawn of War + Steamworks = Ass
Of course, Dawn of War can also be added to "GFWL" making:
Dawn of War + GFWL + Steamworks = Bothersome Travesty
Mathematics degree level stuff, there. Don't feel bad, it's a common mistake on the first try with these complex values.

Don't forget:
Dawn Of War + GFWL = Travesty
And the infamous:
GTAIV + GFWL + Rockstar Social Club + SecuROM = ****ing ********.

So far I've found Steamworks in terms of friends and multiplayer decent. Sure, it could be better, but it's better than Team 17 doing their own servers which could either work fine or be a total disaster. Plus, by releasing it on Steam, people will instantly see Worms in the Steam Store, so it does reach out to a lot more people.
Don't get me wrong, Steam can be a bitch sometimes (DRM, Friends list going down way too much, Region restrictions), but otherwise, it's a decent service. It sure as hell beats LIVE or Securom.

I have the PSP versions of Worms and I love it. A Steam version with achievements would be epic.