1) Referrer obscuring: If I wanted not to enclose referrer, I'd have told my browser not to do it. (I don't want to disable this so I don't like some sites forces me to do something very similar by their design.) 1a) (Rhetorical question:) If you were site owner and were interested in incoming traffic, would you rather see 'someportal.com/outgoing?yoursite/page' or 'someportal.com/certainpage' referer header in access logs of yoursite/page?

2) Phishing protection: assuming such outgoing links are checked with Safe Browsing API or something similar (I doubt it), again, that's what my browser does by default. (Incidentally, sometimes I do not want my browser to do this either, so again I like to switch this off: things are a bit faster and free disk space bigger sometimes.) It might seem nice that some page makes this effort too, but again, I don't see a big deal in it.