Suggest-a-Purchase doesn't locate the Blu Ray edition because Amazon generally only carries that format as part of a Blu Ray/DVD/digital copy combo pack, a format our vendor doesn't carry. However, as you have already selected Blu Ray as your preferred format in the Suggest-a-Purchase drop-down menu, you can go ahead and select the DVD edition from the Amazon database list, and it will appear in the Blu Ray category when our media selectors view your suggestion. Since the item will appear in the Blu Ray category, our selectors will know that your preference is for the Blu Ray edition, and will search our vendor's inventory accordingly.
An alternative way to make your suggestion would be via the text box (to access the text box, click twice on "refine your search terms," located in the upper-right hand corner of the Suggest-a-Purchase search page). If for instance, you had a particular Blu Ray edition in mind, suggesting via the text box would allow you to make that specific request.