The NFL ATL site has posted the official franchise and transition tag numbers for every position now that the salary cap is finalized:
So Jared Cook stands to make an extra $4.5 million in 2013 if he can get tagged as a WR instead of a TE (To be fair: Cook has not said publicly that he will challenge to be tagged as a receiver). If this were a year where the Titans were strapped for cap room, I would suggest that they let Cook walk rather than tag him as a WR, but since they aren't, it makes sense to go ahead and do it either way.
Either way, the Titans will be paying Cook based on potential. There is no doubt that he has the tools to be a dynamic player in the NFL, but it is still just potential at this point- and we are 4 years into the experiment.