A few weeks ago I reviewed the documentation looking for specific mentions of 7.1 or 7.2 features. Primarily they were incremental additions to the APIs based on early feedback. Below is what I found from scanning the documentation. I don't have a RokuTV with 7.0 firmware nor a 7.1 device to confirm, these are purely from the documentation.
@monkeysource - i have not used it but got peripheral impression that 7.0 was not ready for prime time, i.e. not something to target for. Seems to me a sane version would be at least 7.1 or even 7.2. Till then there is no global component, no parameters in function event handler nor message form of it, it seems.
My general impression is that Roku firmware is a moving target and nobody at the Co's side has interest in supporting "older" versions. Thus my suggestion is: try to get answer from developer at roku.com on when new firmware will be available on NowTV - and which version?