Once upon a time, there were a couple of options for “e-commerce”. A large Amazon.com type site with native credit card processing on site, and the small but reliable button to leave the site to go to the Paypal page to complete the transaction.
If you were going to use sell a product at all, you would need to install a large shopping experience such as OSCommerce, Zencart or Magento. Or, for Drupal 6, you would need to install Ubercart. While these were all fine solutions for large shopping centers, the small business person might have felt alienated by the large scale stores and months of development to look forward to, even with Drupal.
These days, 3rd party processors who make it easier, distributions like Drupal Commerce Kickstart, and contrib modules using those have made it more manageable to get started selling for your business with Drupal 7, whether using a store or just writing a module to connect the accounts when customers click “buy now”.