Having a seat all to yourself during rush hour is an impossibility.
From what I have been told, Beijing's bus network is still seriously short of capacity on suburban routes.
The majority of vehicles used on shuttle buses for the Olympics have now gone in operation with city routes or remained with the shuttle routes as they became permanent city routes, and very few made their way onto suburban routes.
Route number resource is severely scarce with only the 900 series being allocated to suburban routes and some routes, such as the 930 and 938, with as many as 11 variations, basically something like 938, 938A, 938B, ..., 938K, until the latter part of last year, when the 800 series were additionally allocated after the authority renumbered the 800 series into unused lower route numbers.
The whole Beijing network consists of, I think, in excess of 20000 vehicles in daily operation with a large proportion 18-metre long artics. A heavily-subsidised flat fare operates on city routes and it's equivalent to 4p with a smartcard, 2p concessions, and 10p without.
The quoted population of 19 million is meaningless as that does not take into account at least another 7-8 million who do not have residential permits in the city.
Oh, and with regard to climbing through windows, it is not something that only happens when departures are cancelled, it is a daily occurrence on some routes, such as the 930 and 938. There is nothing new about it.