OEM's generally do not give you the full install dvd for windows with a new computer. this is true for hp, dell, asus, and every other brand that you can think of. the only ones which might are custom-built. the most many OEM's do is give you a recovery cd but sometimes even this is not provided free. this has been true for well over 10 years.
while i do agree that the disk should be provided, your accusation against ASUS only is unfounded and should be directed at all OEM's instead.
for the record you can create your own windows disk free using a blank dvd. all you need to know is your product key.