"screen" is NOT the default, "all" is... and if you aren't saying
type="screen" in your LINK for your screen media stylesheet, you're pretty much defeating the purpose of CSS. Admittedly I say the same thing about even USING the STYLE tag or STYLE=”” in the vast majority of cases.
Honestly, I'd say any LINK or STYLE tag lacking a media="" or set to media="all" is a sign of the "3i of web development" -- ignorance, incompetence, and ineptitude. It's a sure-fire sign that the people writing any related HTML and CSS are unqualified to do so, much less tell others same.
A contributor to the plethora of reasons that HTML/CSS frameworks are utter and total trash CREATED by people not qualified to even flap their yap about web development.
I'd also mention the "projection" and "tv" media targets that were recently removed from HTML 5, that many devices out (kiosks, Wii, DS) will override your styles with their own if you omit them.
Again, more proof the WhatWG and current incarnation of the W3C are also unqualified to make HTML 4 Strict's successor as they undo 22 years of progress. For every legitimate improvement, they go full Gungan on something else.
Media targets -- device names/types -- should be NONE of the HTML specification's business as that limits what hardware vendors can create. The whole initial idea was for UA makers to be able to make specific names for new interaction types. Instead they've thrown out perfectly good usable ones and limited us to this tiny list defeating the point!!!
But what can one expect from people who were so ignorant of semantic markup they came up with the derpy HGROUP tag (praise be that was killed off) and allowed EMBED into the specification. 100% Hurr-durrz. That the “real” HTML 5 was discarded in favor of the WhatWG’s utter chazerei is so damned stupid, it just proves how useless and toothless the W3C is.
Anyhow since any GOOD inclusion of CSS should already have a media target on the LINK, if you need to say "screen and" in your media queries, you've screwed the pooch.
The same can typically be said of PX metric media queries, since that either means pixel metric fonts pissing on accessibility, or metric mismatches resulting in broken layouts.
Just like the nonsensical notion of pre-planning specific device sizes instead of making your break-points based on the needs of the content. Thinking specific pixel sizes -- 600px, 768px, 992px, etc -- is utterly broken incompetent trash.
Thus your entire "typical device breakpoints" section is a bunch of bad practices that should be pitched in the bin.