As fashionable as it is to deride Flash, the vast majority find it quite stable. I believe a good Flash developer could produce a solid upload client for this service. I also believe that every developer on HN would use such a client without batting an eye.

Granted. Mobile devices are handicapped in terms of embeddable functionality, but that isn't limited to Flash. Java applets, the only obvious alternative for this use case, are in the same boat. I think that if mobile users want to upload >100Mb files over the air it's fair to make them use an app.