Risky? Hardly. First of all, the only new format it can be released on is Blu-Ray because both Lucas and Fox have pledged their support of that format. Second, something as mega-popular as Star Wars could only HELP a format like Blu-ray become more popular. People aren't going to buy one machine over the other because they like a certain player better than the other. They're going to buy whicever one has more attractive media or simply more titles in general.

Now, if they release the box set ONLY on Blu-ray and not DVD, that would seriously impact the amount of sales and most likely wouldn't be worth it. Not to metion the fact that single-disc releases on Blu-ray hover around $30. A box set would probably be close to $150. From a marketing standpoint, it would be wise for them to release it on both Blu-ray and DVD to maximize sales while at the same time helping the success of Blu-ray and catering to videophiles.