As much as we've all waited 20 mins or so for a bus, recall that there are always people who walk up to the stop for that bus about a minute before it arrives. Ask them and they'll say that bus service is fabulous.
One thing to keep in mind - Nowhere does Disney advertise or promote "little or no waiting" for their various means of transportation. In any literature, signage or websites that I have ever seen, I recall Disney always telling guests to allow one hour of travel time from point "A" to point "B" using their complimentary transportation means. While I think this is definitely a "generous" window, I think it is meant to account for "peak seasons", and I certainly am not suggesting that one hour should be the "norm".
As mentioned, my experience with Disney Transportation has always been positive, and I never recall a bus or monorail loop that came anywhere close to a one-hour transit time. For me, most have been in the 20-30 minute range (this includes wait time at the bus depot, stops and travel time to my destination). On a few occassions, I have been on 40 minute loops. Maybe I have been lucky, or maybe it has to do with traveling in non-peak seasons, but my experience spans approximately 20 trips since the 1990's with no horror stories to speak of.
In my opinion, we are spoiled by the times that we get from "A" to "B" in 15-20 minutes, which for me, has been "standard" more times than not. We then get accustomed to these short jaunts and expect them to be the "norm". So when we get that 30-40 minute bus loop, it becomes frustrating to some.
I'm not insinuating that the bus system does not have flaws or could not be improved, but I think some have unrealistic expecations of the overall system. Our OP is complaining about 20 minute wait times, which I find to be well within the realm of "acceptable".