AND proper coding achieves a site that functions identically cross-browser and cross-platform. i manage IT projects for a large media company and nothing goes live if it doesn't work on on every OS/browser/whatever combination covering over 95% of our traffic (and, more importantly, over 95% of whatever combination of browsers and OS leads to revenue... this is why we STILL support that hunk-of-junk IE 7, because users of IE 7 use it to spend $$$). we have an army of QA people seeing to this.

so, while some sites may work better on some browsers, that is the fault of shoddy development or, more likely, shoddy IT management allowing that to happen.

no one builds sites "optimized for browser x" anymore and hasn't since forever ago in technology years. a universal customer experience should be what any money-making site shoots for, and that is what most achieve.

delta's problems with their site reek of compressed timelines and incomplete testing. that's really the only reason that a site may have unpredictable results on one platform or another. developers will get it right, given the time, but other business factors may prevent that from happening and the site's business requirements and design requirements may make it extremely difficult to achieve. those paying the bills are often deaf to the cries of defects or, more likely, some are not communicated up the chain of command for fear of retribution. it all depends on your corporate culture and whether getting it right is more important than getting it now.

in my experience, i have seen people fired for launching a site with fewer problems than delta.com has. perhaps someone there was.