This issue would be more relevant were the batteries interchangeable.
I tries B&D "Firestorm" alongside DeWalt, and found major differences between tool performance as well as battery performance. And, who wants to carry multiple chargers?
It is not uncommon for me to use up half a dozen batteries in cutting a hole for 1" in cement block- the only way I could have enough batteries is if different tools came with them.
Also, some companies have more extensive lines of products that use their batteries. So, maybe DeWalt doesn't have the 'best' cordless reciprocating saw, but it uses my drill battery, charges in my radio, and there's a vacuum available.
Now, there is a role for "cheap" tools. Some, especially if used only occasionally, are worthwhile. I have several. (None are cordless, though).
You can carry brand loyalty too far: why have a Klein bottle opener if your beer comes in cans?
