Scanning artwork certainly has its advantages, but it also has its limitations. Brushstrokes can benefit from a more unidirectional light source. Photographing in a controlled environment allows for fine-tuning of texture and shadows.
Until the past few years, photographing artwork required either a larger sensor or stitching together multiple shots to get printable resolution. With the advent of pixel shift technology in full frame cameras, medium and some larger artwork can be reproduced allowing for better workflow and hence, better value.