Cracked hub
 

Hi, I am considered obese, about 240, 5"11" and have been riding a Tommaso Augusta fixie as my only ride.

I have had issues with breaking spokes and when I took to my LBS they found a crack in my hub.

The LBS said the bike is probably not the best to use on my occational 17 mi commute. He is replacing the hub and I should get bike back within another couple days.

I just ordered a Jamis Earth Cruiser 3 from a Jamis dealer which I will use as my daily ride.

Why is that?

I don't know, you could have probably just put some beefier hubs / wheels and been fine. I know a lot of guys heavier than you that do fine. Sounds like the LBS just wanted to sell a new bike.

That being said, I own a Jamis Cruiser and LOVE it. I still ride it from time to time because it is so comfortable and fun. Enjoy your new bike.

The only spec I can find on the stock Augusta wheels is that they're DP18s on a "flip flop hub". No info about manufacturer, so I'm guessing it's probably just a cheapo hub. As in, not even Formula grade.

The DP18 is a good rim. Bring it to a shop and have it laced to a decent hub with DT Swiss Champion 2.0 spokes, or Competition 2.0/1.8 and you shouldn't have any issues.
I weigh 235 now, but I've been as high as 255 on my fixed/singlespeed bike. I have a 1991 Wolber T410 Alpine rim laced with Champion 2.0 spokes to an IRO fix/fix hub and I've used that bike on century rides.

Your size and weight should matter. You are marginally harder on equipment but not that much.

The larger issue...and the reason that the hub cracked...is the broken spoke issue. When a spoke breaks, all the energy that is stored in the spoke has to go somewhere (elementary physics) and it will go into the hub. The hub can take a lot of punishment but it can crack if hit often enough. A new wheel is warranted but not a new bike.

Have a set of wheels built with DT Alpine III spokes by a good wheel builder. Your troubles will be over.