Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
The idea behind the build, and believe me it works is to actually be able to do some damage with your HGs to grab a few lane kills on top of your normal support role.
Late in the game your spells will do large enough amounts of damage that even your nooby teammates will be able to jump on those you manage to isolate from the group with well placed HGs/slows.
Mainly, I don't think you really need any more regen than the locket and to think your really ever going to be able to take any kind of damage is being naive, so I choose to just use the rest of my items to increase my AP for both improved shields and extra damage.