It's a legitimate issue just like the cracks in the fender aprons. The newer models have a different setup on the bracing to solve this but if you have one of the affected years yeah, inspect it. I've personally seen 4 now and the last one we almost didn't catch the issue b/c the cracks start where you cannot easily see them without an inspection mirror. It's an easy fix and if you wheel it's worth doing. The last one I mentioned was on one of those "little old lady's" and she'd only ever seen one trip through the Sierra's in the snow this past winter, her rig's less than 6 years old, and it never sees abuse, we were just lucky to catch it before her warranty went out and could send her to the dealership to have it fixed under warranty. It's how they're welded, just like how my 2nd-Gen 4Runner might eventually tear at the base of the link mounts on the differential..just one of those quirks that not everyone will see but is worth checking anyhow.
not sure about welding to High strength steel(all newer Toyota frames), its not like mild steel, were when it cools does not loose any of its strength, HSS will get brittle, thats why when the the frame bends on these things, they are replaced...but I could be wrong, thats what the auto body schools taught me at Farmers Insurance