I was at The Strand a couple weeks ago and quite enjoyed browsing, and I found several books that I would like (including a wildly out of date book on dinosaurs with amusing illustrations from their used section).
But in my small shoulder bag I already had a relatively large and heavy hardcover book from Forbidden Planet next door, and I was planning on doing several other things in the city that day and didn't want to carry around anything else... in my bag I also had my small Sony e-reader though, which has never been a problem to carry around when I want to.
On the one hand... books are really not a tough sell in the NYC market. The fact that The Strand is always packed full of people attests to that. But since space is at a premium and you do a lot of walking in NYC... e-books (on small devices) are also not a tough sell! So I'm not surprised that they put this up, but I think it probably isn't really necessary.
I have actually found the prohibition of e-readers (among the most benign of electronic devices) during takeoff and landing quite annoying... I was flying a lot for a couple years a couple years back, and that's why I got the thing in the first place (around 2009 when they were pretty new). I usually am not too provocative on planes but shortly after I got it I was engrossed in something and kept reading as we prepared for takeoff on my Korean Air flight, and a flight attendant came over and politely asked me to turn off my "electronic reading device", which I still find amusing.