Is it normal for newborn to be awake for 4 hour chunks at a time?

[EssexWelsh]

My DS is nearly 3 weeks old and has already got himself into a routine of feeding every 3 hours at night and pretty much sleeps 9pm til 8am each night only stirring to eat but during the day he is awake for 4 hours solid, sleeps for 4 hours then awake for 4 hours, this is fine as he's not crying only slightly whingey towards the end of the 4 hours, it's just that every book and website says newborns wont stay awake for more than 45mins at a time and also encourages 3 hour cycles of eat sleep play if you want to get them to sleep through the night later on, does this matter? Should I be manipulating his routine? How do you do that? I find it impossible to wake him when he's out cold or to get him to sleep during a 4 hour awake window, he just does it when he's ready!

They are all different- they haven't read the same books!
He has his own routine which sounds fine- especially the solid night's sleep.

In fairness he's got himself into a routine from only about a week old just a very odd one for a newborn! But not complaining as sleeps well at night, just stirring for feeds but being awake for 4, even 5 hours at a time seems crazy but he seems happy enough, so we're going with it!