Gregory's ServerI think the crucial part of it is that he's also generated consistent valuable microcontent.
Some Twitter faces I've seen here have just been firing off a handful of very niche micro-blog statements ("I went for a walk this morning, it was snowy") or publicity copy ("my comedy tour is starting, dates and places on my website!") and expecting an audience to engage.
Mas.to's local feed (to a lesser extent now) was filled with that content from randos - it's not valuable.