For example, I regularly work with no less than 7 different OS combinations (OS X, OpenIndiana, Windows, Linux, OpenBSD, iOS, FreeBSD), and don't hesitate to recommend different ones in different circumstances.
To recommend software or hardware without at least passing knowledge of the merits of alternative solutions is frankly negligent. For example, I don't have any Android devices (mainly because of the software upgrade issues), but I know situations where I'd definitely recommend them.
Living in a tech monoculture, whatever it may be, isn't healthy.