Indeed. I buy wards on every back (sometimes two or three on a single back if I didn't upgrade my trinket), but nine times out of ten, the ward amount ends up being 70% Support, 25% me, and the other three players fitting into the last five percent with unupgraded trinket wards. I only see upgraded trinkets from the rare intelligent player, or when everyone has full build. I've even come across people at full build who deliberately avoid upgrading the trinket to piss everyone else on his team off.
While I'm not shocked that people have connected that the jungler is everywhere, he should also carry a Sightstone (possibly stemming from how sometimes you get a tank jungler or Lee Sin carrying one in their builds), I'm a little shocked about how long it took to go from Support only and everyone flames you for doing it too, to the jungler gets demanded he too carry a Sightstone.
As for my ADC comment, the only role that is literally one champion type (and even limited within that type) is the duo lane carry, aka ADC, and of bottom lane. Every other role, meta, and tactic can pretty much be anything. But that team member is different. It's the only one that has never changed for fifty-seven months (since mid summer 2011). I've even seen Marksmen as Supports, but I have never seen any other meta where the carry wasn't a Marksman (even during the double bruiser kill meta, Marksman+Support was still a pretty dominant strategy). Nowhere in the history of League has a real Marksman recommended to purchase a Sightstone. By anyone. Even if ahead, it's the only role where the community vehemently doesn't like a Sightstone in your build. Everyone else could build six Ruby Sighstones for all they care, but if you even think about building one and people find out, you're getting nine reports (or more). It's something I never understood.