He's referring to the inner front apron, not the fenders.
The cracks occur where the front apron has the crumple zone crinkles, about 10" (rough estimate) from the firewall. Basically cracks can develop from the flex forces at work on the front frame section.
It's more prevalent on the FJC's because of the frame to firewall dimensions combined with the newer metals used. It's been addressed with the 2007-2008 FJ's and I personally have never seen or witnessed any 79-95 vehicles experiencing it, except when the situation revolved around someone winching themselves over a very steep section fully loaded when they should have just used the bypass. (Truck was literally "hinged/levered" over the rock.)
I've never heard of it happening on our vintage mini-trucks, but I suppose it's possible. I think a lot of it depends on how the truck has been used (and abused).
I remember seeing a video somewhere on the 'net where they took a brand new stock Subaru WRX and started prepping it for rally racing. The first thing they did was completely strip the car down to a sheetmetal shell, then they welded and gusseted every body seam. This was to keep it from cracking apart. Then they started building the internal roll cage.
Its a known issue with the FJ. If you don't have them, you will and 2007 didn't fix the issue. Mine is a 2007 and its cracked pretty good. I don't heavy four wheel with my truck, just fishing and hunting trips on forest roads about 3 time per year.
Anyway, if you know of folks with FJ, let them know. I'd be willing to bet many folks have the problem but don't know it. A slight bulge is the beginning (barely noticeable, followed by a large bulge and cracking.)
I have no cracks in my cab or inner fenders, I've inspected everything thoroughly now that the cab is totally stripped bare. But, I found several cracks in one of the doors that I pulled out of my parts stash, the cracks we on the inner door panel, 4 or 5 of them or so, about an inch long each. I put some tack welds on them while I was patching those mirror holes. Really weird, it was only on the driver's side, the passenger side was fine.