you can say the same for every position, you don't need good DBs if your front 7 is great, you don't need a good front 7 if your DBs are great you don't need... ect.. a good o line don't mean much if your QB and HB is crap, a good QB don't mean much if your O line sucks, Truth is dude you need a good team, if you start ignoring positions cause you don't need them to win you're going to suck.
If your QB can't throw a good out route teams are going to make him throw outs, if you don't have good WRs teams are going to make you pass. If by week 10 our starting WRs are Stanback and Hurd i can promise you'll see that having good WRs is more then a luxury