I think the idea behind multi-stage dryhopping has more to do with the peak effectiveness of the aromatic dryhop oils being released is more like 3-4 days and not 7-14. The problem with this concept is that even though the dryhops have offered as much of their aromatic oils as possible in the shorter time frame, 3-4 total dryhopping days with only one stage of dryhops is not enough. The IPA would still benefit from an additional stage (or two, or three) of brief 3-4 day dryhopping with completely new dryhops for further concentration of intoxicating aroma. There is also the inconclusive belief that if you dryhop for longer than 5-7 days, the hops will start to release some flavors of vegetalness. Some never experience this result, but as a precaution it is one of the reasons that it's recommended to remove and discard the old dryhops each time you add the new set.
Like you mentioned jim, multi-stage dryhopping probably does have a little bit to do with ensuring full dryhop exposure with the beer and thus making each addition smaller instead of dumping in a ½ lb. of dryhops at once. That makes sense. But it also has to do with making the flavor & aroma so potent that it knocks you off your feet.
I employ a similar multi-stage practice when I make my Sangria, which I make in multiple gallons for parties. Let me explain… Instead of leaving 3-7 day soggy, awful, old fruit in the pitcher for the duration, I will add fruit for 2 days, remove it, add new fruit, and repeat this process three times. This creates an infusion. And each time I remove the old fruit, I blend it and press the liquid back into the sangria so nothing goes to waste. Instead of getting a cup half full of soggy fruit, you get a cup of sangria with tremendous fruit flavor and 3 pieces of fruit for garnish. This technique ensures optimal flavor and fruity aroma, plus your final fruit addition is added fresh, which looks better, still has crunch to it, and tastes better. There are no downsides except it is a little more time consuming. But this can be seen as an improvement on the usual method.
Some say that the best way to allow full dryhop contact with the beer is not to sprinkle them directly atop the beer. Rather, it is to weigh down a fine mesh bag of pellet hops so that it bobs in the middle of the beer with 100% exposure. You have to find the right type of bag that can give the pellet hops room to expand and have full contact with the beer. The best type of bags are the larger, fine mesh drawstring bags that you can tie to the neck of the carboy for ease of removal. Oxygen exposure is limited with a smart setup. Though, it is often recommended to flush the beer with C02 for further protection. Vinnie knows the science behind all of this and mentions it in an interview, which should be online. I wouldn't say he just does it because he liked the results or read a brief description about it in a book like most of us.
All-in-all, this is a very nit-picky way of dryhopping, but some people are fervent believers in it. I'm sure some people have different ways of going about dryhopping and their beer's aroma is still amazing. This is just one of many methods.
![Craft A Brew - Safale S-04 Dry Yeast - Fermentis - English Ale Dry Yeast - For English and American Ales and Hard Apple Ciders - Ingredients for Home Brewing - Beer Making Supplies - [1 Pack]](https://m.media-amazon.com/images/I/41fVGNh6JfL._SL500_.jpg)
