Looks like you too haven't understood what I was saying
It is NORMAL that you can't compile SDK 2.3 on MinGW, because MinGW uses recent GCC compilers, which are the same as the Linux compilers. Compiling SDK 2.3 on MinGW is just as if you were compiling it on Linux. And the problem is that the guys at Valve were using a pretty outdated version of GCC to compile the SDK on Linux.
That's why SDK 2.3 does NOT natively compile on Linux, and that's why it cannot compile in MinGW too - because the Linux/MinGW compilers are recent ones.
That's also why, you shouldn't use the normal SDK if you want to compile it on MinGW, but Will Day's SDK, because he fixed a lot of things in it to have it compile on Linux. And if it compiles on Linux, it must be pretty close to compile on MinGW too, since they are the same compilers.