Agreed. .040 is the absolute limit, as far as I'm concerned, and I wouldn't even go that far given the number of available 5.0 blocks laying around. It's possible to go to .060 on some blocks, but core shift makes it a sketchy deal, and heating problems are likely to ensue.
It's probably to market to all of the people that think that those 4 extra cubes are really going to make a difference in the total power output. I'd guess that half the people I've talked to at work about performance engine work brag about their engine being bored as if it was a performance improvement. Unless you've got something like a Dart or Man o' War block where you can bore the cylinders out to something like 4.125, it's not going to make any real difference in power output.