While shopping for Warré hives on the internet, you're likely to see statements like "the top bars are removable to comply with most/all state and local beekeeping laws". The most likely reason for suppliers to say this is that they don't want to put in the time and effort that it takes to offer you a modified Warré hive. The fact is, many states have antiquated laws that require beekeepers to use framed hives. In the early part of the 20th century, many states recognized framed hives as being essential to keeping healthy bees, because they allowed the hive to be inspected more easily for disease (this was mostly in comparison to using skeps, not other alternative hive types). Therefore, many states at that time passed apiary laws requiring beekeepers to use hives with movable frames. In these states, any type of top bar hive is technically illegal, whether its top bars are fastened to the hive body or not. We don't care how you choose to keep your bees so long as they're healthy, and it's likely that your state's apiary inspector won't care either. However, he or she might care very much. You may want to call and ask. At minimum, you should know what the requirements are in your area before you buy, so that you can make a decision that you are prepared to live with.
Tip: You might be in compliance with your state apiary laws by only having one frame in each hive body. Check the wording of your state's apiary act carefully.