I'm wondering whether the reputation limit in combination with a global clock doesn't create the following effect:
"The quality of the answers is the highest around 00:00 UTC and drops until 23:59 UTC." - idea
The rationale behind it is that each day, at 00:00UTC a new "SE day" begins. So everybody has zero reputation that day. But as time passes, more and more (high reputation) users earn the maximum reputation limit. The result is that some/most of these users don't have an incentive anymore to answer questions (decently; no insult intended at all). So the number of potential answerers (as well as the answerer-quality if reputation is a good measure) drops.
Of course the claim not fully holds: people live around the global and most people won't answer questions in the middle of the night, simply to earn some reputation. Still there is probably some effect... Let's assume people work 8 hours everyday (and consult the site occasionally through the day), then the last person that become active on the site the first time that SE day does this at 16:00 UTC, so from that moment, the quality should start dropping significantly. Furthermore it depends on the concentration of IT-minded people on the globe (one expects the quality to drop faster if people in San Francisco, California are at work, since the concentration of programmers is higher in these regions).
In other words, the best time to ask a question is around 00:00 UTC (based on probability reasoning, and probably later that day based on actual data). This can create problems, since most programmers don't decide when they want to run into trouble with their work. And furthermore people living in different countries are differently aligned to the global time.
A possible solution to the problem - if any - could be that the "SE day" depends on where a user lives. There are probably some issues because users could change their location to tamper with the clock, but perhaps other solutions might work as well.
Please note that I don't claim it is the "intention" of answerers to answer less questions. It's more a subconscious process that people tend to put less effort in things where they don't receive (immediate) rewards.