What does the customer gain from having a web interface you have to navigate to by IP rather than a simple external storage device that shows up like a flash drive?
I think one reason for the web interface is that the device stays usable. If it would export a block device then it would need to unmount the file system on itself or at least block changes. If I remember correctly in the old days before MTP, all Android did this, making storage on the device itself unavailable while making it available via USB.
Yeah, that would be an issue with presenting the device as a block storage device.
The web interface also has a couple of other advantages: the tablet simultaneously listens for ssh connections, and can be used over Wi-Fi, IIRC? Though it could also expose a "USB HUB" with both the network interface and block storage.
I just wish we had a more ubiquitous "network file storage" protocol. The tablet itself could offer NFS, but mounting it under different operating systems would be a pain, requiring manual user intervention.