I'm not going to start a debate, but I can only say from my experience, that theory is totally wrong.   For reference I run my own print house out of my home, and DPI is excruciatingly important.

The Major reason for this, is something rendered and worked in 300 DPI remains, 300 DPI, no matter what size the image actually is.

72 (standard) dpi is perfectly fine, if you render out and create your image in the precise size you want it.   However imagine if you will, rendering out something 24x36.   Considering time constraints,   that is totally not a feesable prospect.   The DPI becomes increasingly important depending on the "stretchability" you want your image to have.

If you render out  a 2x4 image in 72 dpi with amazing details, then place it in photoshop, try this experiment.  Change either the dpi, OR the size to poster size, say, around 18x24, or set it to a base of 300 dpi.  Now look at your image.

What you will see is horrific pixilization, just tiny little squares.  This is precisely why artists who sell their art put up thumbnails and samples in extremely poor quality save for web low dpi...... so that it cannot be stretched or printed out with any kind of copyable quality.  The more pixels you cram into a square inch, the less quality is lost in reproduction and printing.

Usually, no print house or print graphics company will accept anything LESS than a minimum of 150 dpi, 300 is preferred, and over that is exceptional.

Lastly, a poser user who uses post work, such as I do, requires a higher DPI, not just for printing.   To detail and hand paint and do most post work, its impossible at a low dpi, as if you zoom in to say, an eyelash, its indiscernable and just a blob of hazed out pixels, not an eyelash.

Edited P.S.:  I realize you are saying that if you arent printing it you don't need it.  However, as I stated above, truly, you do.   I'm not sure if you have poser and work with it, but rendering takes a lot of time, and to render something out say, in an actual 8x10........ or heaven forbid poster size, would take hours upon hours.   Even so, if you went through all that, if you tried to zoom in in photoshop to detail an eye, the dpi is just way too low to get that kind of clarity you require.