Your example is extremely clear-cut, but doesn't match the situation with Heroku very closely. If Heroku promised an intelligent router, but then it was always down and never served you any requests, that would make your Dell example a good analogue.
A closer comparison might be: What if Dell shipped you a laptop that they advertised as having an SSD with really good performance (and they thought that was true, or at least they did when they wrote the ad for the laptop), and it turns out that for your workload the performance isn't so great? Would you expect a refund then?
I think most people would expect a refund in that situation. However, wouldn't a better analogy be like if they advertised an SSD and shipped an HDD (allegedly without knowing the performance difference), and also the diagnostic tools that they shipped just happened to not report the additional latency (allegedly without knowing that it would be a problem)? Then customers had to figure out on their own that it actually was an HDD despite their documentation and diagnostic tools saying otherwise, after wasting tons of time trying to figure out why performance sucked?