Well there's a difference between signal strength and performance (as in speed). When your device is reporting 2 of 5 bars, 3 of 5 bars, etc., that's reasonably accurate in terms of signal strength. What's fictional are the ASSUMPTIONS made about speed based on that signal strength.
In the case of Windows, sometimes it reports only signal strength (e.g., perhaps when running a wireless survey to find a wireless AP). But once the connection is established w/ that AP, it may now report speed (e.g., it shows as 54mbps, or 33mbps, etc., in the system tray). It's that translation that's almost always bogus.
The reason it’s bogus is because Windows is not actually measuring the performance, it’s simply “guestimating” what the speed *should* be under ideal conditions for the given signal strength. But as we all know, we don’t live in an ideal world. So these estimates are typically vastly overstated. In fact, they’re pretty much useless.
If you want actual speeds, you need to measure it using tools like NetCPS, Iperf, Qcheck, etc. If you report those results instead, then we have something to work with (results that are invariably far, far less than reported by Windows).