The difference seems to be the intended market for the passes. The 10 Day are designed for visitors from the UK and the 30 Day are typically sold in other nations such as Germany, Australia, and the Netherlands.
For some reason, Paramount sells these from Orlando and will sell them to people anywhere in the world. They seem to be the only company that can/will sell them outside of their intended markets. The only other places that sell them are travel companies in the above-mentioned countries and they may or may not sell them to people outside of those places.
I don't know why Paramount is allowed to sell them, but they've been doing it for a while. I assume Disney knows what they are doing and haven't shut them down.
Last year, I met a bunch of people from Australia who were on vacation and they mentioned that most people in Australia get 6 weeks of vacation a year, so they tend to take longer and further vacations than North Americans who typically get two or three weeks off. I assume that Disney recognizes this and sells the 30 Day pass to try and convince the Aussies to spend as much time as possible in Florida with WDW as their base. I would think that the other nations where these passes are typically sold are similar.
Those of us in North America aren't supposed to know the deals that Disney makes in other countries. We're supposed to stay blissfully unaware and buy our 7 Day PHP's and be happy with it.
I bought a 30 Day Pass from Paramount for use on my trip this fall - it was the best value by far considering I won't be going back within a year and needed more than a 7 Day PHP, plus I was already planning on going to Kennedy, so that's another $30 I saved.
Obivously, I haven't used it yet, but everything I've read said there are no problems with using it regardless of where you are from - and there is nothing written on the voucher itself that places any restrictions on its use (other than an expiry date in 2004).
