Anarki_Hunter: The solution for the STEAM and Patch 1.3 is present in the STEAM forums itself, have you checked the steam forums! (facepalm)..
Incase you have bandwidth to download the game again, follow the below steps as mentioned from the steam users forums
1. Delete all the game and files related to Witcher 2
2. Download the game
3. Patch to 1.3
4.
DO NOT VERIFY THE INTEGRITY OF THE GAME, ELSE IT WILL GO THROUGH THE RE-DOWNLOADING LOOP AGAIN. Highlancer: Your /facepalm, caps use and overall attitude won't impress or help anyone.
It happens that I actually did visit the Steam forums for the past days now and there is no official fix (don't tell me about workarounds) for the issued problems.
Also some people can't "increase" their data bandwidth on the fly. We are also talking about 17 GB of game data... (include the initial optional bonus content of 5 GB data).
For a full priced game that people did pay for, you can't admit that your "workarounds" are the solution for such annoying problems.
So it is problem with Steam!, so why is the issue being mentioned here in GOG forums.
Contact Steam Customer service/support, if you have an account in Steam and are a subscriber of digital downloads in Steam..then wouldn't contacting steam support be relevant.
The issue you are facing isn't first kind, there have been other games in Steam in the past and that is how steam works.
When ever you buy a game in steam, you don't own you..you license it. Steam manages your content (for which you have brought your licence) and it is Steam's responsibility to provide this support to you (the consumer who have brought the licence) with its dependencies such as DRM, AntiCheating hooks, etc...
Back to Witcher 2 <-
Since you have brought the licence to play Witcher 2 via Steam to access the content(ie..you brought the game to play), it is Steams responsibility to give you good access to play Witcher 2 from its platform.
What if you didn't buy game from Steam?..There are other ways you can get Witcher 2 where there have been no issues with respect to patching..all other Digital downloads are working fine, All Retail DVD's of Witcher 2 is working fine. Yes!
So!..compain to STEAM that the game they have provided is not working/accessible properly from their Steam client/platform. Just because Steam has its own unique way of protraying access to content it provides , doesn't mean that is the content developers fault if it didn't work in Steam.
My cousins in states, friends in EU have brought Retail DVD's of Witcher 2, no issues for them..since the game is not sold in Retail DVD's in my region, I got the game via GOG and its working fine.
Where is the problem..its with Steam itself (How the Steam content is accessible to you..the customer/consumer).
I also assume porting the game deployment to Steams requirements costs time, someone has to work. Currently I am kinda sure Steam wants to push this costs to the Game developer, instead of them spending the cost because its the issue with their platform.
--forget all the crap I typed, sent mails/requests to Steam support. Until you don't do that, steam will never take random stray requests into account and not fix it on their end. As long as you brought the game on steam, they will never show face..until people shout their problems/complains--
-Edit-Added-
If you are unsatisfied with Steam services, I think you should read Steams Terms&Conditions and check if you can go via legal process with the help of a lawyer to file a case/sue them for not providing proper service, cause additional waste of time and money over service/content provided on their platform void of functionality. Also causing other problems, such as requiring the non-functional content to be re-downloaded exhausting your limited access of valuable internet bandwidth (if you are in a region where internet bandwidth is low overall, then this is very very serious).