Inkjet ink cartridges can dry out through lack of use although it's far more likely the print heads will get clogged from disuse first. Inkjets clean the heads by forcing ink through them, which can use up a lot of ink. Those are the major reasons I will never ever own another inkjet. I had one for a year before I got fed up, tossed the printer as high in the air as I could into the dumpster (it made a most satisfying clunk when it landed), then got a laserjet. Though expensive to buy at first and the cartridges aren't exactly cheap, laserjets cost less per page to use than inkjets, even after factoring in the initial costs.
New printers are notorious for coming with "starter" cartridges that are only partially full. How full they are (or, rather, aren't) varies from manufacturer to manufacturer.