While you're right that expats fill up their passports quickly (I went through 16 pages while interning in Singapore for six months), a case like you describe above would have border crossing cards for both Singapore and Malaysia and would not get any stamps on his daily commute. Those sixteen pages I mentioned only contained two Singaporean stamps - one from when I first entered, and one from when I left for good. Between the two, I did not get a single stamp on numerous entries/exits because I had a border crossing card, issued as part of my work permit.