Is pagination of the data (as shown in those examples) mandatory? It seems kind of annoying to have to limit the amount of data actually in the browser at one time, especially if it's done for "performance" reasons.

Pagination isn't even necessary if you load chunks of the table as needed. You can even render proportional scrollbars if you know how large the table should be.

The trirand grid that you linked to doesn't even get keyboard or mouse focus right. It doesn't even get row selection right.

If you think that's a good grid, I don't expect you to see anything remarkable about the grid I posted.

The most remarkable thing about the grid you posted is that it won't run on my computer. In fact, it won't run on any of my computers.

Looking around my office, I gather it would run on about four or five computers out of the about 50 here.

Fine. Let's compare it to any native grid that runs on your preferred OS then.

Both of those work fine here, and there are a half dozen other jQuery grids available if you want to try them out.