i guess it might be down to the fact that they've never needed it to do more than it does.
most probably, originally the limitations we see today were there as a design decision based on considering the time that would be needed to compile an average map on hardware that was around in the hl2 days vs how much of a difference it'd make to the result.
as far as i can recall of valve games (even the newer ones like the l4d series) there aren't really any cases where a scene demanded much from indirect ambient lighting. - so i guess it's just down to an "if it's not broke don't fix it" mindset together with the LD only focusing on scenes that won't suffer from the shortfalls of the system.
i've found a bit of success though by mixing together the suggestion about the vmt reflectivity values together with the -extrasky compile option on vrad.
Quote from MinosIf you use values such as .5 .5 .5 etc that means your texture map is gonna bounce white color only.
from what i've read, the reflectivity values are a multiplication of the base values of the vtf, so .5 .5 .5 for a surface that is pure red should bounce rays that are pure red at 50% intensity of incident