OK, put another way...
Whichever "maker" or "makers" Delco was using was making crap batteries. For YEARS. This doesn't mean ALL batteries from said maker or makers were bad, just a large chunk of the ones that Delco happened to spec out.
An AGM battery does not leak. Ever. You can mount it upside down, for that matter! Downside is they do cost more, and can be sensitive to deep discharging (even moreso than a lead-acid battery) unless designed as a deep cycle battery.
If cost weren't an issue, GM would be smart to just use AGM batteries in all of their vehicles. On the C5, evidently the cost of warranty returns hit the point where it was cheaper to use an AGM battery than re-engineer where the PCM was located. I would also take this as a strong hint that GM knows the problem is not the bolt since replacing a single bolt and a cheap battery would be cheaper than an AGM battery
As we owners are well aware, GM is definitely "cost conscious" and will often spec something cheaper even if it only saves them a few cents per truck (my, it sure is dark inside my glovebox
It's not a new problem. And I will not be shocked in the least if a 2015 GMC Pickup STILL has the same problem