I'm pretty sure that a significant portion of programmers are night owls and don't like showing up before 10 AM.

I'm pretty sure that people are different and there are plenty of programmers that are the exact opposite.

Well, it's great that they are not forced to show up late then.

"on time" is a relative term. Assuming you show up, work your time, make your meetings and commitments and be a reasonably accountable person - no one will care what time you start the day whether it is 5am or 10am.

This is just not true.

There are offices that have legitimate reasons for requiring employees to be there at certain times. I've worked in secured locations that were all but inaccessible at 6:01 pm and you needed a good reason to be there after 5. In an environment like that, you can't stroll in at 10:30 because you prefer to sleep in.

A lot of folks on HN seem to have this idea that as long as you show up it shouldn't matter what time you get there, how long your lunch is, when you leave, or how many hours you are working vs. sitting on Facebook, and there should be this pure meritocratic judgment based solely on the quality of your work. Maybe that's ideal, but it's 100% unrealistic. In an office environment, showing up on time, not leaving early, and not taking a two hour lunch should pretty much be the minimum.

There are certainly exceptions as you mention, but if there isn't a good reason then why bother with it? This seems largely within the cultural spirit of programming; if there is tedium/bureaucracy, automate it away or solve it with technology.

For me, it's a necessity. I have fairly severe circadian rhythm problems and getting to work earlier is asking me to be unproductive, depressed and tired.

Certainly there are exceptions to what I said - there's always an exception. But I think the picture painted in your comment is the exception, not the rule.