There's scant few articles on going from Python to R...and I think that has given me a lot of reason to hesitate. One of the big assets of R is Hadley Wickham...the amount and variety of work he has contributed is prodigious (not just ggplot2, but everything from data cleaning, web scraping, dev tools, time-handling a la moment.js, and books). But that's not just evidence of how generous and talented Wickham is, but how relatively little dev support there is in R. If something breaks in ggplot2 -- or any of the many libraries he's involved in, he's often the one to respond to the ticket. He's only one person. There are many talented developers in R but it's not quite a deep open-source ecosystem and community yet.
Also word-of-warning: ggplot2 (as of 2014) is in maintenance mode and Wickham is focused on ggvis, which will be a web visualization library. I don't know if there has been much talk about non-Hadley-Wickham people taking over ggplot2 and expanding it...it seems more that people are content to follow him into ggvis, even though a static viz library is still very valuable.
Also worth pointing out, he's actively working on a new book for ggplot2, which, AFAICT, he's providing for free (you just have to run the build tools)
I think if someone were to run an analysis of Wickham's Github activity, it would produce a freakishly busy chart.
I used to work a lot with R many years ago. I was shocked to find how bad the documentation was, and worse how rude and unfriendly the "community" of grumpy professors was. I shudder to think of the horrible meanness towards beginners asking questions on the mailing list.
I got so fed up I even wrote a book about R data visualisation. But this was all just around the time ggplot2 came out. Unfortunately I stopped using R soon after, but since then Hadley has single-handedly done more good for the language than anyone else.
I don't know what the R community is like now, and whether people like Hadley have made it friendlier, but it's clearly one reason Python is superior.
On the other hand, there seem to be a lot of useful libraries that haven't been ported over to Github or are otherwise easily accessible beyond CRAN...Many of them probably don't get as much exposure as they would if they were more easily discoverable...and I honestly don't even know where, in those cases, to start the bug reporting/patching process. That's obviously the fault of my being spoiled by Github...but that's kind of the point, there's a bit more friction in contributing to R than you might find in Python/Ruby/etc.
The caveat on the ggplot2 book is that building it seems to be really hard because of the nightmare of cross-platform latex. But there will be a physical book out early next year.
Every language has third party packages that are primarily the work of one person.
I'm sure your statement is true for some definition of deep but I don't agree.
This isn't to say that there aren't other programmers doing brilliant work in R (also, R is just a smaller community overall), but he's devoting significant time to building out support tools and frameworks...this suggests that he is a total mensch, but also that there was a significant need that hadn't yet been addressed.
Another interpretation is that R is an incredibly productive language for this sort of programming, otherwise one person couldn't write so much useful code. ;)