1.) No, it is not possible to have TechTracker omit paid software or paid updates. See #3 below for one of the most significant caveats to such a feature.

2.) In many cases, the trial version is just the full version without the product key. Thus, if you've already registered the application on the computer, you can simply install the latest trial version and the program will remain registered; no special download or re-registration required. However, that's up to the individual program's developer(s) to provide.

3.) Usually, a 3.0 purchaser would receive 3.1 as a free minor update but not 4.0, a major update. However, some programs come with free updates for a specified time period after purchase rather than based on product version. Thus, no one would know if the update is free for you or not unless they knew the expiration date of your individual upgrade period. That makes it nearly impossible for any third-party to say for sure whether it's a free upgrade for you, individually.

4.) If the updated version of a program only officially supports XP, then the earlier version you have installed must be the same unless the program's developer made a mistake or very odd decision. For instance, if MySoftware 1.0 supported XP through 7, it wouldn't make sense to have MySoftware 1.1 support only XP. And if the developer created separate editions for different Windows versions, such as MySoftware 1.0 (XP) and MySoftware 1.0 (Vista & 7), there would be separate listings in CNET downloads, one for each edition. As a result, you'd only see updates for that edition, as CNET treats them as separate products entirely. Regardless, most programs designed for XP run perfectly well under Vista and 7, even if the developer does not explicitly state so.

5.) None of that is designed to entice users to upgrade for one simple reason: nothing noted here changes between the free and paid versions. All of the points you made depend on the decisions of the third-party program's developer and information known only by you and (usually) that developer. Thus, unless all developers voluntarily supply detailed product/licensing information and all users (such as yourself) provide all information regarding purchases/installations made, there will always be limitations to the effectiveness and customizability of updater applications.

John