Welcome to the modern world. In the old days, when the proto-Mozilla roamed the Earth fighting Internet Explorer and other monsters, cross-browser, cross-platform testing was essential if your web application had any hope of serving your users.
In these days of well-debugged CSS it’s easy to get lazy and figure if you see it work, then it’s working.
However…
I just ran through a number of screens on http://www.linkedin.com – a well established company with uncountable global users, many important screens lacked a “submit” button in OS X Safari, which appear when one uses OS X Chrome.
Really? Making your users go through all that data entry again because you don’t even know that your web forms are broken?
Sloppy.
I know you can do better. Get with the program, people.