If you can squeeze grease out, water, sand, dirt etc. can get in. You don't need to go boggin to get dirt and crap in a cap. Just driving down the road will do it.
The advice given here is not for you, its for the op so I'm not sure why your arguing the point other then justifying your purchase. You'll be hard pressed to find many that will recommend the joints you get at Autovalue when the OEM Spicers can be had cheaper, require little to no maintenance and last a hell of a lot longer.
If you like em, great. But there really is no need to defend your choice, your choice is not the topic of discussion. OP asked for advice, and he's getting best advice out there, that's all there is too it.