It's a little bit tongue-in-cheek for them to say (and me to repeat), I agree… But when you get much smaller than atoms, you're starting to get into particle-wave duality and stuff, where things don't really HAVE positions. But maybe the LHC will spit out something new to right with, who knows?

As to the atom sizes, yes, He has a smaller diameter than Si. But, you can't write on a He surface. It's also specific to the atomic force microscope that it spits out Si atoms. So maybe we'll invent a new microscope that uses a smaller diameter atom.

Personally, I dislike the idea that we've reached some kind of limit, here. I prefer to think that we have no idea what we'll be capable of in the future

It's a little bit tongue-in-cheek for them to say (and me to repeat), I agree… But when you get much smaller than atoms, you're starting to get into particle-wave duality and stuff, where things don't really HAVE positions. But maybe the LHC will spit out something new to right with, who knows?

As to the atom sizes, yes, He has a smaller diameter than Si. But, you can't write on a He surface. It's also specific to the atomic force microscope that it spits out Si atoms. So maybe we'll invent a new microscope that uses a smaller diameter atom.

Personally, I dislike the idea that we've reached some kind of limit, here. I prefer to think that we have no idea what we'll be capable of in the future

That is an incredibly naive statement. Firstly, “atoms are the absolute smallest things stable enough to let us push them around” that we know of right now.
Secondly, these are silicon atoms. If you use carbon atoms (one less electron shell) wouldn't it be smaller? Or helium (two less electron shells)?

Bah!