Amino acids and some peptides are able to self-regulate their time in the intestines. An example of this is the digestive hormone CCK which, in addition to regulating appetite and satiety in response to food[10] can also slow down intestinal contractions and speed in response to protein.[11][12] CCK is released when dietary protein is present, and demonstrates a way in which the body can slow down digestion in order to absorb all present protein.[13]

In a study done on women, consumption of more than 54g of protein in a single meal versus across four meals resulted in no differences.[25] As these women had on average 90 lb of lean mass, it is highly plausible that more protein could be efficiently processed. The same researchers found that a single high protein meal was actually more effective in a population of elderly women.[26]

30g of protein?
There really is no literature to indicate this number as a 'holy grail' of protein absorption.

It may have arisen from looking at the rate of amino acid transporters, assuming 10g/hour as a standard, and applying that to the typical mini-meal approach to bodybuilder nutrition (with a meal every three hours).