i enjoy your post but i dont’ agree with this note:
“When you start using breakpoints, forget about setting breakpoints at standard size resolutions or displays. Set you break points where your design starts to actually ‘break’.”
I think is quite difficult to mantain a responsive web site with no-fixed breakpoints; breakpoints gives you the necessary constraints to design and develop responsively. Without fixed breakpoints everything is a mess and your CSS begins unstable while the project grows.

Zurb Foundation is an excellent css framework that takes care of these size problems for you in a sensible way that doesn’t leave you in a reality bubble of designing only for a family of minority market share deivces.

I believe, from a device agnostic design approach we need to think in terms of what’s best for the design and not get consumed with the PPI or resolutions of each device – design stuff more fluid and device independent. I kind of think that if Apple chooses to make the touch area smaller in its iPad mini VS the iPad with Retina than as long as our buttons scale nicely they will fit into the user experience that Apple has designed for there device. It’s cool if the design and/or experience is a little different in these two devices because the device is a little different itself.

I don’t think you’re missing the trick and this is exactly why we should start designing more device independent… we can avoid these issues of PPI and 2x resolutions and all that. Like you said, the problem with trying to design for devices and their differing PPI’s is that you will eventually start to end up things that look weird in certain devices because you compensating for other devices.

This is a great topic… I think I’m going to carry this idea of fluid, device agnostic content into my next article and dive deeper into it.

Thanks Sarah!!!!!!!!