*Role* needs to *do something*!!!
They mean ranked. They are talking about play to win, which is ranked. Let me explain some:
So, I am seeing this argument pop up... and it has been for a while. There's always going to be some argument and counter argument over who should buy what.
Big thing? Supports and sightstones (I support main, I buy sightstones because vision is important to me).
But here's my argument: If you play ranked then please play to win (you can also play to have fun, this is a good idea, but keep in mind that winning should still be your goal). If you play normals: then play to have fun. If you don't want to build sightstone, then don't: it's normals. That's why it's normals, so you can play casually. If you want to play hard to win: play ranked. If you play hard to win and can't win in ranked because of a horrible team, but can normally win normals - you aren't that good and need to accept it, but continue playing ranked because that's play to win and that's where you'll improve. And ranked is where people want you to play right, ranked is where people want supports to buy sightstones and top to have TP. Ranked is where people expect you to play the game in the expected fashion, normals is for everything else.
When people complain about This role needs to buy this item or this role needs to do this thing they are talking about ranked. If you don't play ranked then please don't argue what people should or should not do. Take the advice if you want, and if you want to say that something works for you in normals, then please say so. There's a huge difference between normals and ranked (maybe not per game, but consistently they are different) so it's hard to compare.
As for supports buying sightstones:
As a support you are not just supporting your ADC getting kills, but supporting your team (your ADC is just the one that helps you get going). Supporting your team means you need to help them, and vision is a TON of help. So are pings, and healing and CC, damage can be helpful but there's already roles designed for damage so don't try to fight that one. If you can do damage + cc or healing, then by all means go for it (and ADCs relax some if your support gets kills on accident, it happens), but don't just take a high damage champ because that's what you want.
Again, this goes for ranked really. If you want to duo ADC bot lane in normals, go for it - you might win. Jinx and Tristana might make a decent match against the Mundo and Vayne you ended up against. In a ranked game it's not likely to turn out in your favor though. That's why this advice fits for ranked. Want to play your best in normals, or just practice? then use the advice! Want to just play around and pick any champion anywhere? Go for it, it's normals! Just please don't use the argument that "I play Shaco support on normals and never ward, therefore supports do not need to buy wards all the time." because that same logic in a ranked game would end up with significant losses (if someone can prove me wrong, please do. I'd love to see support Shaco without wards be successful.)
Oh, and to say it: If you are playing to win please play ranked. If you want to play off-meta champs just remember that there's a reason for the meta and that off-meta champs aren't likely to win as often which is why those are played in normals and you can't be upset about losing.
TL:DR; Tips are for play to win. If you play to win, play Ranked. If you play normals, don't complain about people having fun.