Just because Davis lines up @ X, Y, or Z doesn't mean he is going to be the primary target. The threat of he lining up anywhere could be because it opens up the passing offense more for other targets. Davis has been used more as a decoy than I can count.
This is a good point. Davis can beat even double coverage, so the defense has to respect him.
Like chinawildman pointed out, having Davis line up in the different spots will open up a lot more plays, as well as free him up to get more space within the passing offense as a whole. Yet even not being a target on smaller plays, his speed and blocking ability can free up a RB reception because he can line up anywhere and block, and creates more dynamics for Kaep's read and progression.
That is the reason why Davis was drafted, that he has size and speed, could line up anywhere, and create a more dynamic offense even as a blocker. It's old hat. The quote of "I will do anything they ask me to do" is so Mike Martz's 2008 offense where Davis said the same thing when called to block more than be a threat. He said that back then too. Martz had similar ideas and promised the same with Davis back then in the pre-season and camp by featuring him more within his offense. Of course, you need a QB with that offense, and Martz didn't have them. So thus Davis in 2008.
I hate Martz because he eventually ruins offenses built by others, yet he did create an offense with lesser parts and with Shaun Hill at QB. Of course we all knew then that it spelled Davis' potential numbers to sleeping with the fishes, yet that season with Martz really helped him become a more complete football player.