We discussed it, but ultimately decided not to. It certainly would've impacted the cost of the unit, and there are plenty available for relatively cheap on Amazon that would serve most peoples needs.
On the water, the reason it's not mentioned is because it really depends on the water you use (and some are running a water/coolant mix). Using distilled water will be fine for a very long time, but using tap water, you're likely to start to see build up in the water lines if the unit sits unused for a decent length of time. If you're using distilled water, you can go over a year without changing it, but a year is a good interval to go by.