Perhaps a better DTTG app would have a version of DevonAgent inside of it. That way data could be collected on the web pages using command buttons. Taking notes from web pages while on an iPad would work just like on a computer. Switching to Safari would not be necessary.
Look at what 1Password did. They have enabled web browsing from within the app that can access input features of the app that can not be done using Safari.
I would be glad to hear that anything is happening with DTTG, but the signs seem to be that it (like Devonsphere) are to remain fairly quiet projects.
Alas!
Declan (hoping to be contradicted)
You can do this somewhat now with DEVONthink To Go, although it works so terribly that it is useless. If you sync a URL, you can browse within DEVONthink To Go, make a text selection, and then click to popup a Copy and Capture clip. Selecting the Capture clip will attempt to capture the selection to the Global Inbox, however I’ve never had this work where it actually captured the entire selection. There is also the problem that one cannot enter a new URL to browse from, which is even more limiting. I don’t know what the developers intended with the Capture function, but the functionality doesn’t deliver. Hopefully an update is in the works?