I've seen those tweets, and I didn't think much of them at the time. Everyone works out and does what they can to get healthy and fit. I don't see what Crowe's problem is. So what if he has a bit of a gut? Does that mean he's never going to work again?
When a male actor balloons up in weight--and Val Kilmer is the actor who comes to mind as I write this--it isn't the end of the world. I suppose there's a segment of the celebrity-infatuated population that probably has the fits and giggles over it for a minute and then moves on. Crowe is a big guy. He is always going to look a little dumpy and like he just rolled out of bed, especially in shorts and a polo shirt.
Crowe is merely dealing with aging and the things that go along with it. He has famously put on weight for various roles and doesn't really seem to care what people think of him. Why he has to publicly battle his own weight and push the requisite tweets out there from time to time speaks to how image-obsessed people get.