The difference between web and biotech startups is risk.
For a web startup it is easy to build a product that works. Hire some talented programmers and designers and you will have a working version of your idea. The risk lies in getting people to like and choose this product.
For a biotech startup the risky part involves going from an idea to a finished product. A possible treatment for a disease should work well and be safe. But hiring reputed scientists to lead the development phase is no guarantee to prevent the complexity of biology from threatening your startup. Once the product is finished, adoption by customers is easy.