I'm no apologist for CO. I think the fees are all bullsh*t. That said, you are incorrect in that the fees are more or less the same across the legacies and Plats are exempt. Regarding change fees on award tickets:
CO - $150. Plats are exempt.
DL - $100. Plats are exempt.
US - $150 ($250 for transatl/transpac)
AA - $150, though date and time can be changed for free. Don't know about exemptions.
UA - $150, though date and time look to be changeable for free. Changes in connections, though, explicitly trigger the fee. Don't know about exemptions.
(Thanks to an FTer in another thread who I copied some of this from.)
I'm switching to CO from NW/DL because of their new 3-tier award structure that is essentially a devaluation. My wife has been gold on CO for years and we have never had a problem getting int'l biz award seats at the saver rates. That said, their taxes/surcharges/fees were much higher than I'd ever experienced at NW. However those rosy days at NW are long gone (or going..) and I think CO is a very viable option. I'm sure I'll be complaining about them in a few months though.
Whattdya gonna do, huh? It sure feels like the golden age for frequent flyers is past.
peace,
~Ben~