they limit the number of books/troops that can be finished each hour.

as stated before if you train 1000 troops 1 at a time they would all be completed the same hour.

and the same goes for science. its just a small advantage but in order to use it you had to script it. so for server load purposes i fully understand that they dont whant to split 1 request to train 5000 books in to 5000 requests to train 1 book.

its no dos attacks its just "exploits" to gain a minimal advantage