I think BU are putting their catalogue titles out on Blu because they already own the rights to them. I think that's why so many studios are 'playing it safe' by not buying new titles, plus there are only so many titles that can be bought or have known masters. It would be nice to see other undiscovered films get a release but often their rights are too expensive or the labs have no idea where the films actually are.
Maybe once the economy picks up BU and others will start putting out lesser known titles again. Theres still a load of gialli to see the light of day or to be re-released by another studio, there was all the NoShame titles that must have expired rights.