Often they aren't (hence short lived components, great variability in longevity from installation to installation, etc.).
If you have a Bryant Evolution Thermostat (or it's identical twin with the Carrier badge) you can get some useful measurements pretty easily. One of the key "figures of merit" for such a system is the "static pressure" essentially how well does air flow through the system (the lower the number the better, less "friction". Numbers larger than 1 are very bad).
If you have one of the current Evolution Thermostats, open up the panel and locate the button marked "Advanced" for a very, very long time. It will eventually come up with a screen you probably have never seen.
If you select "setup" you can "reinstall" the system, which includes a calibration run (this takes several minutes, as first it polls all the devices in the network, and then finally gets to work). You will have to verify the various devices (typically just say yes, but if the installer accidentally left you with some devices unconfigured or configured ones you don't have, make the necessary adjustments). Eventually it will do the calibration run, which only takes a minute or three.
It will report the static pressure in "inches of water" (you'd have to ask someone else why that's the unit of measure). 0 is impossible, about .5 is good and if you have some of the fancier filters you may well see .8 or .9. If you get a higher result, try again after removing the filter media (you could have a clogged filter). If it's still high, you probably have a problem in the ducting, especially near the furnance.
With modern multi-stage equipment, the peak value (which the installation/setup program is discovering) is only part of the story. The other bit, is what's happening at any given point in time. The "Advance" menu let's you see the ongoing static pressure, speed, various critical temps (see the "Service" menu).
Needless to say these options aren't covered in the version of the manual they hand out to homeowners.
So if you have an Evolution or an Infinity thermostat give it whirl. Let me know what you're results are. If I get enough data, I'll post a table.