Scirra dev here. This is indeed a problem. The thing is Chrome is ultra-strict about the MIME type and rejects it if it's wrong. Firefox seems happy with it. Given HTML5 is new and nobody has their servers set up with this MIME type, and lots of people are already making HTML5 games with our tool, I'm tempted to say it's Chrome's fault for being too strict... getting everyone to reconfigure their servers is a real PITA just because Chrome is fussy.
Ah - well I guess the spec is written with the future in mind when everyone's got their servers configured correctly. Until then nobody has their servers set up right so I think it would be practical for browsers to be a bit more relaxed. Right now we're seeing a lot of games on servers without this MIME type, and the browsers respond by requesting all files from the server all over again every single page reload, probably wasting a lot of bandwidth and making HTML5 games look bad. I think there's a good case for a bit of relaxation on the browser side - standards compliance is good, but not if the web isn't ready yet.
No... just no. If browsers are relaxed now, then they are forced to provide backwards-compatibility for all the sites that then rely on those relaxed standards. Why do you think Internet Explorer is a complete mess and have dug themselves into a whole of having to ship half a dozen "compatibility modes" with every new version of their browser? Because they didn't stick to standards.
Every single piece of documentation about appCache mentions the requirement for the correct headers to be sent. Chrome isn't being "ultra-strict", its been in the spec since day one.
