Just played on a silver elo account, played top lane 20 times, and got camped all 20 of those games, regardless of how the lane was played out. Played on my D5 main, no one ever funnel ganks top lane because they understand that camping a tank role is completely useless.
Why? Because Top lane has the most distance between turrets, and only deals with one opponent in most cases. Bot has predictable warding and few real gank angles and often full pushes in. Mid has a low distance between turrets and people usually stay on their side of the lane.
Top is the basic choice.
It is true that it makes more sense to roam all lanes while doing your farm rounds, but that's second round logic that Silver players don't get. Also, they probably have bad experiences with ganking bot; In Silver 90% of bot ganks are completely unreactive. You can give a bot lane a time stamp of when you will gank and ping 20 times who you're targetting, and go through an unwarded angle; They will still ignore the game and afk farm. Or worse: They are always dead when you reach bot rotations.
To add to what Illabethe said (as a noob jungler who doesn't stick to one lane): Now that I think about it, It's better for learning how to gank since you don't have to focus on which lane to be attentive of. And because one is roaming less, they have more time and opportunities to gank and learn how to gank in the first place.
I'm not a good player, so It get's messy/hard to track where to be while learning. I've been trying to learn jg by properly roaming, but by doing so, my inexperience in ganking in general often opens me up to getting killed when I try to help.
Seriously, learning JG is difficult if every other JG I play against knows even a bit of what they're doing. I honestly die less roaming to mid early game as a support (ie. Janna) than I do trying to gank bot lane as a JG.
It may be time for me to consider this "focus top" strategy for the sake of learning.
