The moment that there's a second person, your life begins to depend on their schedule, involve their input in plans, etc. Even if you're the boss, it's a terrible habit to just declare you're leaving without taking in to account how it will impact other people. I'd argue you're probably /more/ restricted in many start-ups than you are in a typical office environment, where you're just one of many, because of how important you, personally, and your involvement is likely to be to the whole team/company.
Many of the points also only apply to people who are doing software for execution on servers or apps or similar projects. If you're working on embedded hardware, for instance, it becomes much, much harder to just take your laptop and work somewhere else.