If this is true, then why do:
1) many MP games ban log bombing of capitals and the infrastructure around capitals?? It is usually justified as a gamey tactic to destory the source of the whole armies supply distribution - hence log bomb the capital and starve the army, certain death.
2) what legitimate reason would anybody have to send an army to surround ANY capital .... and then refuse to attack or capture it, just sit there and have a picnic? If you surrond a city or capital it is for one reason, capture, not to surround it and do nothing?? It presumably does have an effect on supply to the army outside the capital or it would not be done (though I don't claim to have the tech knowledge of reading the code).