I know that Airline Revenue Systems are more complicated to understand than the meaning of life, but can anyone explain the following:

LHR-LAX
2nd March 09, returning 12 March 09.

BMI Price/BMI Code Share on UA Metal: £280.70. WLXBD2.
UA Price/UA Flight #'s/Same UA Metal: £502.70. WLXELF25.

Obviously different fare basis even though both are W fares - is this just BMI trying to sell early fares? Surely they revenue share with UA on this?

Furthermore, an infant fare on BMI is only an extra £32.70, whereas according to the UA website you have to buy a child seat if flying International as an infant?

Obviously my money is going to be going to BMI, as there seems no benefit whatsoever paying UA direct for this, just looking for some clarification if there is some for these results?