Regardless of how its implemented, the LCL has it as ownerdraw and its not the only windows type control the LCL is doing this too.
The fact remains that its doing it and does not match the native behavior of windows, which can be correct..
Also, if you look closer at the existing code, it looks like it may have had the DT_EXPANDTABS in there at some time because they are using #9 and later using the DrawText function. So its my opinion that it wasn't always like this.
Have it your way, I am only a visitor.