Yes, you're right. The common (lazy) approach for companies that don't give a shit is "we own everything because it might be complicated to introduce ambiguity and we own you anyway".

Having carveouts for obviously not-related software is easy. At a decent company populated by reasonable people, if you wanted to work on something you felt fell into the grey area, you would ask and get a written okay. Which is how it also works at many of the shitty companies! The difference is that the shitty companies there's never a route to do anything, however unrelated, without running it by HR. Because they think they own you.

> Imagine after Slack took off, that an employee claimed that because they had written Slack at least partly outside of working hours and it was not "video game software", the company didn't have ownership of the software.

On the contrary, using a nonzero amount of working hours to work on something pretty clearly makes it company property.

> The difference is that the shitty companies there's never a route to do anything, however unrelated, without running it by HR. Because they think they own you.

"Shitty" companies have legal obligations to include these kind of clauses though, because investors and board members don't want to deal with a situation where there's exactly this ambiguity about what counts as "obviously not-related software". HR exists to protect the company. What counts as obviously non-related to you may not count as obviously non-related to a board member who hears about the new optimization algorithm you wrote and realizes the company can monetize it.

> On the contrary, using a nonzero amount of working hours to work on something pretty clearly makes it company property.

How recently have you seen a tech employment contract where you were obligated to work exactly 8 to 5 with a 1 hour lunch break? Flexible hours means any hour is potentially a "working hour".