The idea that marketing can potentially eliminate the need for salespeople depends entirely on context. For example, this may be possible in some B2C situations; however, for many B2B transactions (for example, those involving industrial organizations) this is mostly impossible.
Another dimension is the value of the goods being sold.
Fast-moving consumer-goods (FMCG) require no sales people at the point of sale to get them to jump off the supermarket shelf and into the customer's trolley. However, the purchase of large mining equipment worth millions of dollars will require a salesperson to manage the sales process – particularly in the face of competitors.
Small and medium businesses selling such large ticket items to a geographically-disperse client base use manufacturers' representatives to provide this highly personal service while avoiding the large expense of a captive sales force.