Actually I counter checked the license terms during installation. The following paragraphes are part of the license terms:
«THE SOFTWARE MAY INCLUDE PRODUCT ACTIVATION AND OTHER TECHNOLOGY DESIGNED TO PREVENT UNAUTHORIZED COPYING. THE ACTIVATION TECHNOLOGY MAY PREVENT YOUR USE OF THE SOFTWARE IF YOU DO NOT FOLLOW THE ACTIVATION PROCESS DESCRIBED IN THE SOFTWARE AND DOCUMENTATION.»
and
«2. Software License. If you obtained the Software from Adobe or one of its authorized licensees and as long as you comply with the terms of this agreement, Adobe grants you a non-exclusive license to use the Software in the manner and for the purposes described in the Documentation, as further set forth below. See Section 14 for specific provisions related to certain components.
2.1 General Use. You may install and use one copy of the Software on up to the Permitted Number of your compatible Computers;
[...]»
This is the standard Adobe license terms. Especially the Section 14 does not contain any mention of restriction due to the download version and their keys. At no point in the license terms is a mention about the need to have purchased a prior version in order to be able to use the «free» CS2 version.
People have obtained both, the software and the keys through an Adobe web page (which is still up and reachable), which does not contain any further mentions about any license term changes.
According to this, and the license terms shown during installation, the fact that people access the Adobe download page to download both, the software and the keys, makes the software legal. Unless they change the terms and/or restrict the access to the downloads + key, there's nothing they can do about this.
http://forums.adobe.com/message/4976620#4976620