Corporate insiders (officers, directors, and employees) need to disclose trades involving their own company.
I don't believe an individual trading his or her own money need to disclose anything to the SEC. I could be wrong though.
https://www.sec.gov/answers/form13f.htm
For smaller companies it can also come out in a 13D which is faster (within 10 days), but only if the investment is more than 5% of the company. That's why there are a lot of ownership stakes of 4.9%.
Interesting, I think it's the same percentage in Indian stock exchanges.
Is reporting speed really important enough to change the size of your investment?
I wonder if this is a sign of the internal politics at BH as 85 year old Buffet gets closer to retirement/death. The younger guys want to make their mark and betting on a typically galloping horse like Apple is a nice way to start the pissing contents with others wanting to run BH after Buffet goes. If Apple does a massive rebound then the guy who made this call will be seen as the young whippersnapper who 'knows tech' and can take BH into the 21st century.