Web Reports - Custom Report vs Explore Computers

While using Web Reports, I noticed that the following in a Custom Report:

<?relevance (number of bes computers whose ((now - last report time of it) / hour <= 24)) ?>

Was showing a much larger number of machines with a Last Report TIme under 24 hours, than when I checked Explore Computers and looked at the number of machines with a Last Report Time less than 24 hours old.

If I put a Web Reports filter on either of these, the numbers would be close or match.

Is there a difference in the source of the results of these 2 methods of pulling data? Custom Report as opposed to Explore Computers?

Is it wrong of me to expect similar numbers when comparing these 2 methods?

NOTE: The Custom Report actually checks on a couple of difference time ranges for Last Report Time, but used one of the Time Ranges as an example.

Thanks,
Bob_K