It's really all about factoring. You'll notice now that you have model logic in your controller. If you want to reuse that elsewhere, you'll first have to extract it to another class. That class is effectively a SQL generation library, except it's not useful in a general sense and it's not as well tested. The more you do this, the more you converge on reinventing a full blown ORM.

I'm not saying there aren't downsides to ORMs, but the counter-arguments to SQL in your controller are pretty obvious.

You'll get none from me. Funny reading your post, because it perfectly describes my own experience this year: starting to learn another language (ruby), then getting pulled right back into php for a big client project. And I also decided to ditch ORM and stick to PDO, which by the way is one hell of a library.

Couple of small things: you shouldn't `return ($var);`, since that returns the result of the statement `($var)`. Use `return $var;` instead, and return them by reference where possible.

I also would have gone with naming consistent with PDO's (i.e. `halfCamelCase` rather than `lower_case`), but that's personal preference. Consistency would be nice though.