I owned a M&P 15 Sport cousin, a DPMS Sportical. It had no forward assist, no dust cover, and also no shell deflector. I fired many thousands of rounds with this rifle, prior to selling it, and this "cheap" rifle performed perfectly. S&W is using the Sport as a lower priced rifle, to compete with the other companies offering similar rifles. Does the addition of these items make the rifle better? In my opinion, none are needed, and they all add extra weight. That is why the price is less, because a few items were left off. If I had a choice of with or without, at the same price, sure I would take the with. That is the decision you have to make. Spend more or get the lower priced rifle, they will both shoot the same.
Just a note regarding pricing. I have seen many Sports selling new in the box from dealers, for well under $550, on the Gunbroker website. Saw one go for $480, a week ago. I have purchased and sold many guns and rifles on Gunbroker, and I have never had a problem. I got a new in the box, M&P 15T, from a gun dealer, 6 months ago, by bidding on Gunbroker. My winning bid was $730 plus $20 for shipping. All guns and rifles have to be shipped to a FFL, but my local GS only charges $20 for the transfer, and I didn't have to pay sales tax for an out of state purchase. My net cost was $770, which is not too bad for a new, $1150 list priced rifle. I spoke to the selling Dealer, and he said he didn't make any money on that one. He said "you win some and lose some", and said I got that rifle for a super low price. I never bid or look at auctions with reserves, as you will never get a good deal with a reserve price. I am not bidding on anything now, but when I was bidding, I would have the winning bid about 1 time in 15 bids. I never get into a bidding war, I set my maximum, and stick to it.
Bob
The Sport is as fine a firearm as you'll find anywhere for the price. Go to the picture thread and you'll find many, many Sports. You probably won't recognize them because we tend to play dress up with them......... a lot. 
