Rick, partition pruning avoids scanning rows in partitions that don't match the search criteria, so your assertion that a query examines the same number of rows whether or not the table is partitioned is incorrect.
There are several examples given in the cited section of the Manual; try running a few of them and see the results for yourself. There's another example or two given towards the end of this
MySQL DevZone article, as well.
Note also that I said (emphasis added), "queries on partitioned tables
can be significantly faster"; simply partitioning a table is no guarantee that queries will run faster, any more than simply indexing every column in all of your tables is going to make your queries automatically run faster. Like indexes, partitioning has to be understood and used properly to see the benefits, and misuse is likely to lead to suboptimal results.
Jon Stephens
MySQL Documentation Team @ Oracle
MySQL Dev Zone
MySQL Server Documentation
Oracle