More ways of using MySQL other than the basic MySQL extension:

1. MySQL Improved
2. PDO MySQL

More data stores other than MySQL:

• SQLite (also SQLite3 in PHP5.3.0+ and PDO)
• PostgreSQL
• Lots more DB vendors/abstractions

Then there might be a time where you want to paginate something else entirely like existing PHP data (arrays, objects). In basic terms, pagination should be able to take a collection of things and break it down into paged sets. Those things needn't necessarily be database query results and the output needn't necessarily be HTML (or the exact HTML that your function uses).