Black & Decker ... the sponsor of the DeWalt cordless line developed the first cordless tools, at taxpayer expense, for the space program. They then were allowed to make the batteries and chargers 'proprietary,' (meaning no one else could make interchangeable replacements) .... and let the innovation wither on the vine.
I had one of the first "cordless drills," and, despite it's princely price, it was complete junk.
Then, along came Makita. Marketing a line of many different tools, with interchangeable batteries, better chargers, and much better batteries, Makita entered the trades like a whirlwind. They pretty much ruled the roost, up to the day DeWalt (then a new B&D acquisition) exploded on the market.
Makita lost its' lead because it had become complacent. They are still - 15 years later - trying to recover from their loss.
DeWalt seems to have learned all the wrong things from these past experiences. Their quality seems to no longer meet expectations, and there seems to be a certain smugness in their attitude. (At a recent 'Counter Day,' the D-Boys had their fancy trailer, but were nowhere to be found).
IF I am not able to use the new batteries with my older tools - I'll just have to buy new tools. However, when that moment comes, DeWalt will no longer have the "common battery" advantage they now have (on my truck). If I must carry another charger, and set of spares .... they might as well be Makita. Or Milwaukee. Or Ryobi.