Yes, in general a bigger dog is going to have more issues. Not always, but in general. And if they have issues, they're probably harder to deal with because of the weight.
Things I've done to try to avoid health issues:
- Not neuter before two years
- Feed a good quality kibble (or raw would probably be better)
- Don't overfeed, keep them lean and fit
- Try to get them to grow at a slow steady pace
- Don't feed too much calcium (< 1.6%, and keep calcium to phosporus ratio at 1.2%
- For the first year or so try to keep jumping, stair climbing and other jarring movements to a minimum
- Get them a moderate amount of excercise
Those are all of the things I'm doing specifically for the betterment of my boy's health.
As for weights, yes it's difficult to judge weight by a pic, but that male looks way too healthy, fit and trim to be 270. He could have a huge frame, but even then he looks too thin (a very healthy looking thin) to weigh that much. Now if the pic is old, he certainly could have filled out from then and could weigh 270 now, but I don't think he'd look like he does in that pic.
Here's the father of my next pup. I really like the look of his head and I do like that he's a "thicker looking" mastiff, but I also think he's overweight and would have no intention of letting my pup get this big. He's 35.5 at the withers, which is very tall.
http://www.stonehavenmastiff.com/judah.htm