Just go a reply from 1kVoice about my UA965 flight cancelled due to mech reasons. I had to pay for extra bag on re-routed LH flight:

Please know when a flight is cancelled and you are rebooked on anther airline, you are subject to their bag polices. Unfortunately, we are unable to reimburse you for inconvenience, loss of time or absorb the cost of unused prepaid hotel accommodations, special events or ground transportation at your destination.

this just makes me mad...