Out of curiosity, how long ago was "a while back"? I've been building on Drupal since version 4.7 (now on 6.14) and haven't ever had a problem with sites break

Out of curiosity, how long ago was "a while back"? I've been building on Drupal since version 4.7 (now on 6.14) and haven't ever had a problem with sites breaking on upgrades within major versions. It's only when upgrading from v4 to v5 to v6 that I've had to adjust my custom templates and modules to work with new APIs. But that's why major upgrades get new major version numbers and are years in the making (and testing).