He clarifies in the comments that the purpose of the exercise was to "highlight teams with a potential surplus of players at certain positions." The idea is to summarize which "deep" teams may be cutting quality players very shortly and which "thin" teams will be signing those players. This has nothing to do with how talented the Seahawks who will make the 53 man roster are.
In that vein, I agree that the Seahawks should be listed as having excess players at RB, FB, CB, DE, DT, and ILB/OLB. I can see at least one player at each of those positions who is potentially on the bubble and yet could contribute to several other 53 man rosters this season.
He omitted safety, but Winston Guy will probably get cut and put into the rotation on a 53 man roster elsewhere. That makes us deep at safety by the author's definition.
I agree that we are "thin" at TE at the author defines it, as I think there is a very good chance we bring another TE in after cuts.
QB is not deep. As great as we feel about the Wilson/Tjack combo, they are not the point of this analysis. When Brady Quinn is cut I think he will get a look somewhere but teams will not be beating a path to his door by any means. We don't have a third developmental QB like many teams, but we don't really need one either.
WR is not deep. Chris Harper is an intriguing 6th WR mostly because we haven't seen anything from him yet, but there are tons of 4th round picks who do not stick on 53 man rosters in their first season. This time last year, everybody was worried that Lockette wouldn't last on our practice squad. When Harvin comes back this will change completely, but there is a reason we spent our first round pick on Harvin and signed him to that $67 million/6 year contract.