I can ride faster than the bus.. but I need to be fresh for work. No point in using all my energy getting to work when I have to 'edutain' 5 year olds by singing and dancing etc for hours at a time. On a commute I generally hold to about half of my potential so that I have plenty in reserve for the rest of the day. On the way home sure... ride as hard as possible.

As for slowing down for one bus the problem is there are 10 buses along the same route. You can't be out of phase with all of them.