Much of 850R said is fine and good pratice (esp. the issue of pH matching) but the issue with the bag being too 'dirty'? Please, you are adding a fish already exposed to what the bag has on it - that is, their aquarium water!
I'm assuming 850R wasn't referring to "dirt" on the bag; he was pointing out that if they use some sort of chemical cleaner on the counters and then the bag gets rested on it, you'd be putting those chemicals into the tank when you float the bag. I've honestly never thought about this before, but I've also been drip acclimating instead of floating for quite a while now.