But perhaps it should include all of those people in coffee shops using Surfaces and ChromeBooks and MacBook Airs.
I highly doubt most modern websites don't support 1366x768. Every front-end team I've worked with tests on iPads and smaller screens. I have a feeling the OP speculating and making blanket stereotypes against designers. But these designers almost always work with front-end developers who take usability seriously and any good teams have feedback loops to correct these issues.