I reread it, It is a little clearer to me now.
The timer on the cpu screen does keep counting, even after timeout. It was kind of a troubleshooting aid so no "stop counting" logic was put in place. The tank mph is based on that, so you should see it start decreasing speed as you slow down and come to a stop. But if you stop more than 7 minutes (or whatever you set it to) then it will reset to the time of last activity at the next sign of activity, no matter how many weeks have gone by (though don't be surprised if you need a jumpstart)
The timeout business is a little tricky, but it is somewhat important so that we do keep track of the time spent at stoplights even (hopefully) with the engine off. Otherwise the time used for the distance traveled for any given trip would be too optimistic. If it takes 10 hours to get from point a to point b, it takes 10 hours.
I don't know exactly why bikes would not track it, but it could be more motivating to see higher mph figures after pedaling your but off, and if that gets you back on your bike then cool
