Numbering is there as an organisational system surely? It makes life a lot easier for collectors and I can't imagine how fans of Commando, TPL SDL. etc. would manage without issue numbers. For a long time, the latter 2 series had no dates. That part of my collecting life would have been much more difficult without issue numbering. So, when DC and Marvel start from scratch again, it might well give them increased sales for a wee while, but it makes life a bit harder.
I think starscape has a point when saying that the higher the no., the lower the quality, and despite Lew's suggestion that Dandy was at it's best when it folded, I'd have to disagree. I tried some issues of Dandy a bit before it's demise with some local kids. Their parents reported that the children disliked it and two of them were frightened by bits of it. My personal opinion is that it was pretty poor stuff. I'm an old bloke so it probably wasn't for me, but it seems like it wasn't for a lot of young readers either.
I really dislike the re-numbering trend in American comics nowadays but, fortunately, as I don't buy or collect them, it doesn't affect me too much. Apart from when talking comics and my ignorance shows up with where various series are. Some folk still think I'm supposed to know all about comics. Truth to tell, I've never had much of a memory for what happened in what number.
I always thought there was something a bit off with many unnumbered British titles. Perhaps not when they were delivered every week, but nowadays collectors must use dates to figure out missing issues on their wants list. Perhaps I'm a bit lazy

Newspapers have numbers or volume + number on the front page.