CS1.6/HL1 require you enable Beta software in steam. CS:S and TF2 are fully released and out of beta status. Looks like Valve are also beta releasing HL1/CS1.6 on OSX at the moment. Also why wouldn't Valve have access to Flash for Linux? Even if the CS:GO HUD is written in flash, they should be able to port it easily enough. it's not like Flash doesn't exist on Linux. Considering they've reached out to Intel and many other companies it's a safe bet that they'd bring a flash HUD over.
No announcement yet.
Counter-Strike Source Now On Steam For Linux