They could save the MGM stuff for it's 90th Anniversary in 2014 (which would also be a good time to put some RKO stuff on Blu, since it's 85th Anniversary will be in 2014 as well).
I doubt WB would legally be able to do a MGM 90th, while there is a MGM company around (who may be doing their own). It's a similar situation to Universal and Paramount this year. Both had Anniversary labeling, but the majority of the true Paramount titles were neglected..
Frankly, the humongous Box Sets are ridiculous IMO, because the are too high-priced for the casual consumer, and most of the individual titles that would be wanted by interested consumers are probably already owned.
As for the non-box offerings, in the new-to-blu list, there are a higher proportion of WB produced titles than from the other studios
And remember, its only a marketing banner. If it bothers you, take a sharpie to you blu-ray case, and problem solved. You'll be watching the movie, not the marketing. I mean, if I had a Blu-Ray box of the ten Fred and Gingers with the WB Shield, I'd be ecstatic.