Kappy what are you talking about, "Adobe doesn't allow that"? Adobe doesn't allow what. They certainly do allow you to download the Demo versions of there software and if you have license number then you use that to make it a Full version and activate it.
I think you got the original post wrong. The OP is talking about Photoshop CS 5.5, Not Version 5.5.
EDIT:
And certainly Adobe gives an Upgrade price on all their software. Most of it you kcan skip at least one version and still buy the upgrade version.
Like I have PS CS5 and I skipped PS CS 6. I will buy PS CS7 and use my PS CS5 license as the Qualifying Previous version during the install.
If Adobe did not give discounts, Upgrade versions, Everyone would stop buying the new versions. As they come out every 18 months.