Yes, it's weird they used 2.0 in the original code too. Doing proper gamma for any regular space (sRGB, YUV Rec.705, etc.) isn't actually that heavy (even without LUTs).
My guess is that the code was written by someone in 1995 back when no one understood color spaces, or something (it's hard to track down who and when wrote it exactly due to all file moves and refactors etc.)