oscar8h, This was discussed a lot in the past...
1. There are a marketing issue involved. Companies estimate the number of viruses by high.
2. There are different counts possible: variants, etc.
3. There is not an international rule for virus naming, so same virus could be consider one or more by other company.
4. Scanning settings are very important.
5. Active viruses (ITW) are really more important then the whole number.
6. Generic signatures and heuristic detections cannot be really counted as 'virus detection'.
Well, etc. etc.
Trust avast!
Many things are detected under same names.
http://www.avast.com/eng/vps_history.html only lists new names.
The number of "definitions" also counts the -gen detections somehow (Trojan-gen, ...) - that are not shown on the history page.
You can say that the history page shows only new detection names, not new detections.