Re: Ah but wait a moment...
Not my Steam downloads :-). If I download at 70 megabits per second, Steam seems to reflect, pretty much, 70 megabits per second in its own speed indication. It's very slightly lower but I'm putting that down to protocol overhead.
Steam also essentially tallies with independent OS speed meter apps (hooking into NDIS) and a bandwidth meter running on my router's interface, rendered in real time through its web interface.
AIUI, to be able to accurately indicate an effective uncompressed download speed for compressed files... which I think would be useless... Steam would have to either 1) know the exact compression ratio or 2) know how far through it was in the compressed files it's receiving with some kind of index or lookup table, which would be impossible or extremely technically difficult (i.e., not worth bothering with) to accomplish.