Anybody that writes Gem's will cry when they can test multiple versions without useing multiple computers or VMWare. Imagine if you could only test your work with one version of Ruby how many bugs you'd miss/hit.
For now, yeah, because 1.9 is still fairly new and not 100% compatible with older Ruby code. I imagine in a year or so everyone will be on 1.9 and this sort of thing will not be need by most people for a while.