The scaling of the gold of the support

I find it strange that a support has significantly more gold, as compared to the team average, on a team that is doing poorly than on a team doing well. Don't believe it? Check this out:

http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/2038086039/211539496?tab=stats

See, my team did really well. And even though I have tons of assists, the 1 gold for each nearby minion that died mastery, and did tons of autos and spells to rack up a lot of gold, I still have a lot less than anyone else on my team.

Consider the contrary, where your team is doing really badly. The gold each member of your team has is somewhat evened out, since you get the global shutdown gold from all of the shutdowns your team gets. Meaning that, yes, even the support has increased gold relative to the average of your team, as compared to the alternative.

Maybe there's something I'm missing here, but I really don't see a good reason why there should be such a discrepancy. Is there some real, logical reason for how this helps the game?