Thanks. So what you're saying is it would be wise to use a database for a task like this, rather than "wing it" from scratch with a file and file structure of my own? Something like MySQL wouldn't be overkill for something like this?
You could use a file-based system, but it does not scale well. For a few pages with a few comments, no big deal. But as you start having to read and parse larger amounts of data from files, it tends to take longer in direct proportion to the amount of data (and at some point may leave a linear relationship and become exponential). Modern databases, on the other hand, are designed from the ground up to efficiently store, retrieve, sort, and parse data very efficiently; so using a DB-driven solution would scale much better.
Therefore, if you see this as never becoming a large site with 100s of pages and 1000s of comments...I suppose whatever works for you is fine. But if you expect (hope?) it will grow, or if you just want to leverage this as a learning experience, I'd go with a DB-driven approach, even if just using SQLite within PHP rather than MySQL or such. If you use the PDO DB extension in PHP, it will be pretty easy to switch later to MySQL (or PostgreSQL or whatever) later, should you decide that would be better for you.
On a related note, for the fun of it I created my current blog specifically to see how simple I could keep it, including no database. I've been contemplating whether or not I want to add a comments facility or not, and so far I've not decided if I really want it, and if I do, will it be DB-driven or not. See https://github.com/nogdog/cwrblog if you're interested.