I have to admit, this isn't a trend I'd like to see spread. It looks like a messy series of arrangements between Maiden's management, venues, and individual ticket sales companies. Leeds Arena/Eventim aren't offering standing tix today, but they don't mention if Ticketmaster still has any. The arena's standing area isn't all that big.
Like Wiz says, though, seats are still worth it. If it's anything like last year, it's a good show, and worth having a decent view. I ended up getting seats for Leeds - thanks Ticketmaster - and I'm quite looking forward to that now.