Dave Noble - in your case CX offered an alternative that was acceptable to you. However, where airlines don't offer an reasonable alternative, if they have involuntarily downgraded pax then there should be some compensation/refund for that.

An analogy would be buying a new 4 bedroom house with decent sized section, only to be told the developer has changed his/her mind and built an apartment complex instead and you have a little 2 bedroom apartment. They haven't delivered on what you bought, and the same applies to the invol downgrade situation.