It may be that some artists are aggrieved when a cover version performs better than their own, but such is life. Alexandra Burke's cover of 'Halleluah' was always going to make the Number One after X-Factor, even though it is a por third behind Jeff Buckley's version, and Len's - in that order - but they all took the top three places in the chart, so Len gets some serious royalties which boosted his bank balance after being ripped off by his former manager - hence his need to tour again in his seventies.
I think all posters have the right idea - some cover versions are just laughable and or horrible, some bring an entire newe dimension to a song, and some franly eclipse the original.
A good song will hopefully shine through, and it may lead a section of listeners to check out the origianal which can often be a good result.