Sandbox

I wanted to write a review on a extension, but my account for the forum didn't work. Why can't i use my account for the forum on the extension site?

And: on the forum, my name is Lenn-art. That name was not allowed by extensions, because of the - in my name. So, there's some difference in registration rules ...

This is by no means an 'official' answer, but here's what I guess is the reason:

The forum is powered by SMF (see footer) and is not bridged with the other official Joomla sites.
There are probably very good reasons to do this. The fist one that comes to mind is that it is unlikely that all 27667 users of this forum will need an account on the extensions site.
As for the unallowed character in your name, I'd suggest you take this to the extensions site forum. That's where the people who manage the extensions site 'reside'.

If you need more explanation, someone from the team will surely provide it.

Have a nice day.

We do not use bridging, to keep all sites and functionality as clean as possible. This is much easier with updating and upgrading, and is much easier to support. The same goes for all Joomla subsites basically.

Joomla itself doesn't allow the - sign (by default). The forum is using the SMF user database, which does not have that particular limitation. The default products are used, so this just means that there is a difference in user creating in SMF and Joomla.