The presale was schedule to run March 30th 10am to 10pm, although I think the link was still up in the morning on the 31st. Don't if it was active then or not. It would appear this be an easy ticket to get selling as there was no instant presale sellout, and tickets were still available on wed for the NYC shows.
Why is the band touring... Well it's a reuniting of the orginial lineu for one. Several current bands are citing Gang of Four as influences. Franz Ferndinand, Bloc Party, etc. There is a bit of Gang of Four lurking in LCD Soundsystem. The Red Hot Chili Peppers has always sung the praises of the band. More politically then the Clash, the spastic guitar rocked by funk inspired basslines set them apart from other post punk bands.