Is it an absolute necessity that they are including? No. Brand usually is enough...HOWEVER...
All companies provide a wide array of quality levels. It's hard to give an exact example, but referring to computers, think about just about any brand...Cooler Master for instance, makes some sub-par stuff, but their upper tier is very exceptional.
So is the manufacturer using a $0.10 cap, or a $1.00 cap?
And in the instance of some quesitonable capacitors in a PSU, it can be easier to decide whether you want to purchase that PSU depending on which series of capacitors were used. If they used Teapo general purpose, hell no, but if they used some reliable upper tier Teapos, sure.