On the "Available Plugins" and "Downloaded" tabs the UI shows the Homepage in the detail information for the selected plugin; but not for plugins in the "Installed" tab.
Without this, there is not way to determine this information; that's why I've left it as a bug rather than an enhancement. (Other than possibly uninstalling, which assumes you know where the plugin comes from.)
It's true, this attribute are not kept in plugin's metadata, that's the reason why Plugins cannot show it. It's RFE to enrich plugin's metadata (openide/module system) or update_tracking DTD to allow keep this attribute.
IMHO, knowing the homepage information is critical. Without it, it is very difficult looking for support, updates or even usage help. I don't know the rules about priority for enhancement, but I'm bumping this to P2 (and I'll see if it sticks).