Yes, it is completely normal for wifi to disconnect when asleep or idle, or when reading a book. It's to conserve battery power by not constantly running the wifi radio when you are obviously not doing anything with it that requires wifi.
I use DHCP for both my N2E and my NC - they both behave like this, btw. Yes, it can take a moment to reconnect when you go to use wifi for something, but I've never had any issues with my devices making the connection (had my N2E since they first shipped out after pre-ordering, and got the NC last December as a christmas gift - both running the most current updates now). I use an old Linksys WRT54GS wifi-router, connected to a TimeWarner cable modem.
One thing you can do to enhance DHCP connection, is restrict your DHCP range of useable IPs to just as many as you need. I have 10 devices connecting at home and my routers DHCP server is setup to only hand out 10 IPs and DHCP leases never expire - which means that each device almost always gets the same IP, even mobile devices that connect/disconnect frequently.