What’s up with The Gap?

It was a funny thing when I was in London the first time, two years ago. All of the announcements about “Mind the gap.” coming on all the time in the Tube were amuzing to say the least. I saw the gap and didn’t really think much about it as I hopped from one platform to another, barely able to find my way around.
Two years later, the gap remains of course, but I’ve noticed it quite a bit more. For one thing, it’s quite a gap in some places, rising or dropping nearly eight inches. Obviously in an ancient subway system like this, it makes some sense that you’ll have a difference of gappage as new stations are added and new trains brought in to service, but what amazes me is that I was seeing such a huge gap at stations that were new on trains that were new. Maybe they try and match the old stations as close as the can, but then I was in an old train at an old station and while the height gap wasn’t such a problem, the gap between train and platform was enormous.
I’m not 100% sure where they’re going with all of this and I suppose that’s where the joke comes in. In some ways I guess I appreciate it despite the fact it makes many of the stations off limits to anyone with the slightlest of mobility handicaps. Of course, the Bart seems pretty mundane with its matching platforms and trains once you get home.