By beta, you mean "free game for a few months before anyone else gets it" right? Because beta tests are only good for publicity these days. People apply just to play early rather than beta test.
I'm telling you right now I'm going to buy the game. I'll pay for it in advance if Tripwire would like. I'll pay in full forward before they give out beta keys.
By the way, the reason you do beta tests is because it is a test. It isn't for fun, it's to get feedback from players regarding the gameplay mechanics, game balance, map layouts, and most importantly, BUG REPORTING.
I've got about a dozen bugs or exploits in Ost Front I can list off the top of my head. I would have reported them and they would have been fixed pre-release if I had been in a beta test for Ost.
In case you're still confused on why beta testing is so important, go look at Modern Warfare 2 on PC. People are constantly complaining on their forums, particularly the PC forums, about exploits, networking issues, hackers, and game bugs. They also complained that there was no beta and no demo for their brand new proprietary matchmaking service, IWnet. Another case in point, go look at Gears of War 2 for the Xbox 360. It's a raging pile of ***t. Basically it takes forever to get into a game via matchmaking and when you do there is blatant "host advantage," bugs, networking issues, and most of all you have a tendency to skate around the map or randomly blow to pieces (lag). Neither of those games had open betas because they felt it would affect their development schedule.
Beta testing is important, get it through your skull. It ensures a quality product when the game hits the market so I can yell at all my friends until they buy it. People don't like buggy games. It affects review scores, it affects public opinion, it pisses your most dedicated player base off the most, and it affects the lifespan of the game significantly.
There are things you just can't detect in internal testing....apparently, anyway, considering how many games without betas get kicked out the door with glaring bugs and issues.
Edit: I should also mention that Red Orchestra used to be a free Unreal Tournament 2004 mod, so effectively people were playing Ost Front years and years prior to the retail game's release....in fact, if I'm not mistaken, you can still play it. Likewise with Killing Floor....they were both free mods that people were playing before their retail releases.