In your example your wife would have to wait for few second for the network to become functional. Im sorry, but I don't really see that as a big issue. Especially considering the huge benefits users would get in "normal" use-cases.
You are describing a situation where the user is twitching to do something with the computer. Where the user even pre-positions the mouse in order to be able to do stuff as fast as possible. Those cases are very, very rare. Normal users do NOT work like that. Normally people don't start their computers thinking "OMG, I need to get online NOW!". And even if they did, the fact that the system boots in 5 seconds, means that they could get online a lot faster than with "normal" boot-sequence.
That said, I don't really understand the complaing about networking. My OpenSUSE-laptop takes ages to boot. And after it finally get to the desktop, it STILL spends few seconds connecting to the network! It would be A LOT better if it booted in 5 seconds, and then spend few seconds connecting to the network.
It makes sense to exclude networking from this experiment, since connecting to the network is not really part of what we call "booting". It's not up to your computer, it's basically being held back by the network. And hacking the boot-sequence of your computer does not touch your network in any shape or form. Network is completely outside the scope of this test. And just because you do not have working networking for few seconds does not mean that the computer is not usable. And still, the "normal" distros are just as slow as far as networking is concerned, so there are no drawbacks in this experiment, as far as networking is concerned.
So how would your wife benefit if the recipe-machine was using Ubuntu (for example)? Instead of booting in 5 seconds, the machine would boot in 45 seconds. Even if you had fully working networking after that 45 seconds (you wouldn't), it would still take about 30 seconds longer to get online than with this fast booting.
"Secondly, note that Firefox's start up will be slowed down if the computer is also trying to bring up the network"
Starting FIrefox taxes the HD and the CPU. Neither of those are taxed when your NIC is getting an IP-address.
"start printing services"
That could be started when the user actually wants to print. Why should we sit around, twiddling our thumbs, when the system starts printing-subsystem, even though the times we print are few and far between?