At low load it's "close enough" that many people will figure, "We just don't have enough experience at writing Web Services well yet, and the faster development time makes up for that in the meantime." By the time you really understand how to write proper web services, you will probably have either:
  1. found it takes just as much time as your current practices
  2. found that it just doesn't scale under load
  3. committed so much time to the conversion that you'll go ahead with it no matter what, even if that means doubling your hardware installation
  4. all of the above