Once and for all:
The speed listed in the download list is a calculated value, that approximates (better or worse) the _50_-seconds average speed.
OTOH, the speed displayed in the status bar and in the title is the *precise* _30_-seconds average speed.
So, to summarize, why they're different:
1) They use different time interval.
2) One is a calculated approximate, the other is precise measurement.
Any questions? Check the code :)