8th Edition now uses TLoS rules now which makes poisitioning units much more difficult for gaining cover. However, I can see an ulterior motive in this change... People who aren't rich but want to try out different options will end up using proxies against their mates in matches. I can confess to having used pieces of paper divided up to represent that awsome unit I don't have yet in battle. Could this TLoS be an attempt by GW to encourage people to actually buy the models they want instead of bits of paper? Just speculation...
Eh, anything is possible, but realistically, if you're playing with your mates I'd hope they would give you some fudge room with line of sight...
Well most infantry models are essentially the same height so it would be pretty easy to just place one random model on top of your piece of paper to use his LoS, but to bew honest I don't think the finer details of actually needing to measure a 'true' LoS is actually going to crop up all that much in WHFB, we generally don't use anywhere near as much terrain as 40k. I can't say I have ever used pieces of paper, but I have proxied with other models before.
I was told that TLOS was inacted when a higher up in GW went to a gaming store and was watching a match of 40k. He saw that a unit was going to get absolutely blasted in the shooting phase but when it came around the general didn't fire. He asked why and the general replied that there was a forest in the way, and that he didn't have LOS. The GW man was astonished because their forest was a CD with a single tree glued to it, and it was shielding a tank. So it is crappy terrain that did it. They wanted the games to be more epic and realistic, but yes also to make you buy GW terrain instead of having CD forests and cardboard buildings.
See thats an aesthetic thing as well. I am perfectly happy seeing a cd with a tree on it and knowing that it represents a forest thus my guys can't shoot through it, but it sure is easy for them to physically be placed on it if I want to move through which is arguably more important. Now you essentially need to make an extremely thick forest to block LoS, or you can have a forest (still the same 'type' of terrain) that is a tree on a cd and it will not block LoS, but will still provide soft cover and a movement penalty the same as the carefully designed extremely thick forest will. Clasification for types of terrain is IMO better than what you see is what you get.