I've been looking for a shirt EXACTLY like this for months, while expecting my baby!  Under the Nile is the only shirt I found!
The benefits of this design (in addition to the organic cotton) are these: if you practice EC (elimination communication) with your baby, you need super easy and quick access to change their dipe or to quickly put a little potty under them, so they never develop a habit of soiling themselves comfortably.  This shirt is GREAT for ECing your baby.  Secondly, if you (like me) believe that your baby needs tummy time every day for improved lung function, improved strength and head control -- then you also need a shirt without any buttons, seams or snaps on the baby's belly.  And lastly, I of course love the organic, embroidery-free shirt (who likes to have their tender skin scratched by some useless and rough embroidery and irritated by pesticides?).  So, for my purposes (EC-ing a tiny newborn who either sleeps, nurses or poops)  this shirt is perfect.... For a more active baby, perhaps a onesie would serve well (if the riding up of the shirt becomes a problem as they start getting more active)...
But I do agree that the price of about $15/ shirt is ridiculously excessive.