Canon's software was only available for download as "Updates". In order to use the Updates you had to have the original software installed on your computer from a CD. Of course, there are also some registry hacks that can get around this problem and there is also a v.1.0 of DPP available for D/L from somewhere, but there was no "easy" way to get up-to-date Canon software without jumping through various hoops.
This has now all been rendered unnecessary by the availability of a "Digital Solution Disk" that can be downloaded directly from Canon.
EOS Digital Solution Disk Software