they did send out an email about the NA pre sale, people probably missed it because it was the last lines of an email.
I got the email on the 20th
subject:
U2 360° Tour Horizon Presale : Spain, Germany and Croatia PLUS news on first North American presales.
only thing it said about the NA presale:
And if you're looking forward to buying tickets for the North American leg of the tour,
check in on U2.com this Monday - we'll be posting first news of presale dates for Chicago, Toronto, Boston and New York.
I wouldnt expect to get another email before tomorrow morning discussing the NA pre sale. I can see why people missed it though since I dont see the end of subjects that are that long and in the text of the email it wasnt discussed until the very bottom.