Vat/sales tax on space sale for ad in print media

Advertisement in print media involves sale of space by the publishing company  to the advertising agency/person on whose behalf the advertisement is printed.   Advt.  space in print media is exempted from service tax.  Advt,  space in print media fulfulls the essential characteristics of goods, ie, it is having  marketable value, can be  used/consumed and is deliverable or transferred .   Then why sale of  such space in print media is not taxed  under VAT?.