There's actually some anecdotal evidence to back this up. Edelman reportedly worked his tail off with Brady during the off-season while Welker was going through his contract turmoil. Plus, BB has stated that he has improved EVERY aspect of his game over last year. And let's face it: with the ongoing emphasis on tight ends in the passing game plus addition of a legit outside threat in Lloyd, slot receiver isn't as vital to the passing game as before.
Edelman isn't as good a receiver as Welker, but he apparently is good enough that the drop-off isn't catastrophic. Another key is that he's quite arguably a better punt returner than Wes. It seems likely to me that Welker won't be back next season and that Edelman is his (younger) replacement.
Finally, Edelman has shown added versatility playing defensive back AND I would presume he's likely the third (emergency) quarterback given his college background. Add it up and his elevation of status makes sense from the team's perspective while not boding well for Welker being a Patriot after this season.
It might end up that Wes shot himself in the foot by playing hardball in contract negotiations (especially at his age) and not signing a team-friendly pact vs. signing the franchise tag.