We use that 700ft AGL turn to crosswind as stated in the FAA book. I find it works well and I prefer that to turning at 500ft AGL as by the time you get to the downwind, you will already be at traffic pattern altitude (assuming it's 1000ft AGL).
Another point is what happens when you fly a faster airplane into a busy training pattern? You cannot fly exactly the same pattern. The FAA state a turbojet has to be at least 1500 AGL against 1000 AGL for pistons. Even with our Apache dirty, we often have to fly a wider pattern to accomodate local C150s, else we "eat'em up!"
And how about pattern entries? The UK way of 2000ft overhead join seems odd to me. First, all aircraft join at the same point/altitude then it seems to be a free-for-all! (I've seen it first hand on a busy Sunday at Shoreham). The US way of 45 degree join to downwind is a bit more logical although this can get exciting too (we're talking uncontrolled fields here). Any thoughts, hybrids etc?