The raspberry pi hardware has no power management capability. Period. End of story. It does not have a sleep or suspend mode. It cannot not even be turned off. There's either power (plugged in), or there isn't (not plugged in).
When you shutdown the system, the software stops, meaning there is now no way to get it to do anything again. However, the "power state" of the hardware is still the same (because it only has one state, on).
So whatever your problem is, that is not it. You may want to look at your logs to see if anything else has been going on during the network downtime -- eg, (I'm speculating), if you have stuff attached to the usb ports that is near the limits of the pi's 150 mA output, that thing may intermittently fail, and if it's a wifi dongle, the system will then have to wait until the interface reappears. You'd see lots of evidence that in /var/log/syslog or /var/log/messages.
If it's any consolation, I use the pi headless on a WLAN and don't turn it off very often, and it's been pretty flawless. I use this methodology to ensure the connection stays up; peeking at the current log, it's had to reconnect itself only twice in the past 48 hours. However, I make pretty light use of it too, maybe occasionally there is a big download, etc., but not constant traffic (the more it's accessed the more opportunities there are for something to fail, so I can't say how reliable it would be serving a cafe full of people all day). Also, I have it on a 3.8A hub and the only thing plugged directly into the pi's usb is a "nano"-size wifi dongle.
