I agree that when you set the goal you get to pick what counts towards it and what does not.

I also feel that when there are several definitions of a word, you get the pick you one you use.

I don't think you get to make new definitions for old words.

Commute | Define Commute at Dictionary.com

The one I use from this page is "to travel some distance regularly between one's home and one's place of work".

FWIW, I've been car-free since 1999. Under your friends' rules, I get to count every bike ride as a commute. This is silly. I use the definition above. Going to the store and such is an errand, IMHO, not a commute.

For the record, today was commute 201 in 2013, and my 1,592nd consecutive workday bike commuting.

I count all miles going to and from work as commuting miles, even when I take the long route. If the ride starts at home and ends at work, or the other way 'round, those are commuting miles, IMHO.

OTOH, what's really important to me are commuting days, not commuting miles.