I suspect that much of it is due to PayPal fees, etc; but it could go against the grain of people if they think "Yay. BitCoins. No Fees." but then find that they have to pay fees to get traditional money in and out.
At least in my case (CoinPal), PayPal's fees and the associated fraud rates are the dominant factor. I pass through fee decreases when I get them, but they're infrequent and small. I do what I can to reduce the fraud costs, but the service is still young enough that many PayPal payments aren't "mature" yet and fraud continues to trickle in.
On the other hand, I don't know of a solution. I guess all I can do is encourage people providing those services to please try to do it at the lowest reasonable cost you can.
Selling goods and services can earn you Bitcoins with lower/zero nominal fees, but it requires substantial time investment to build the service, build trust, provide customer service, etc. From a strictly monetary perspective, that investment can make the fees look downright cheap. Of course, creating is way more fun than buying and that counts for a lot
