Try the 's' search, which searches the entire topic. Additionally, every GNU Info topic has an index page, which you can do a page-search in (the GNU 'info' viewer has a command specifically for searching the index, 'i', but pinfo doesn't seem to).
he GNU Info documentation format is pretty nice from the user's perspective (once you use pinfo), shame it never caught on outside of GNU. The Texinfo markup language for producing info docs has some quirks (e.g. having to escape full-stops in some situations), but those could probably be fixed.