I've been reading papers authored by professor A's PhD students. I have read about a dozen of papers by now, and realized that all of them are exactly 10 pages long. These papers were written by different PhD students and they were published in several different venues (very good ones). Is 10 the magic number for paper-length? (at least in professor A's field, which is computer science - human computer interaction)
Most American computer science conference papers are precisely 10 pages long, because most ACM conferences have a strict 10-page limit on proceedings papers.
(ACM is the Association for Computing Machinery, the primary professional society for computer science.)
Conference papers often have fairly strict page limits; however, there is no uniform consensus even between different conferences in the same field, and certainly not between fields! For example, one fairly extensive series of conference papers (whose conferences I attend semi-regularly) limits contributions to six pages.
Similarly, many journals—such as "letters" journals—have even more severe restrictions (four or five pages), while other journals have (seemingly) no page restrictions at all: I've known papers in both engineering and mathematics journals that have gone for 20, 30, or even 40 pages.