Jonah,
I'm assuming that you are on version 10.0 based on your question. Data Reviewer will write all the records to the Reviewer workspace. The limitation you are describing is when loading the records in the Reviewer Table dialog. Depending on the user's machine if there are too many results, it would crash Arcmap; that's why we had this limitation in version 10 and prior versions.
If there are more than 20,000 errors and you want to see them all, you can open up REVTABLEMAIN in ArcMap directly. You just won't have the functionality that is provided in the Reviewer Table dialog like grouping and updating correction/verification statuses. But you can get the counts that you are looking for.
At 10.1, we address this limitation so now you can access all of the records in a session even if there are more than 20,000.
Cheers,
michellej.