They could be. Though looking at Phanuel's http://forums.anandtech.com/showpost.php?p=33069727&postcount=8 graph, they correspond roughly to an hour at 200W for a tempo ride, pushing it to 250-300W for a really hard ride and dropping down to 120W for a light ride.Those speeds seem somewhat high, at least for me.
As others have mentioned, I've found the speed and calorie readings on most spin bikes and gym bikes to be pretty far from what I'd normally expect for rides of various intensities.
I suggest we agree on a simple rule of thumb to apply to rides logged on spinning bikes (and to a lesser extent, indoor trainers). Something like 19MPH for a tempo ride, going up to 23MPH for a really hard ride and down to 15MPH for a light ride.
Or just not post at all since elitists will whine about it not being the same thing as riding a *real* bike, even though miles are miles (circumference * RPM, etc) and OP asked for both real and stationary... oh well, not my loss, I'm down 12 lbs in a month, that's all that matters to me.
Does the runner thread not consider treadmill miles to be "real miles" either?