Tell us about yourself!
you could always make mitered half lap joints at the corners and glue those instead of using fasteners. Slightly more work but it's visually appealing and very strong.
Easier to produce perhaps but dowel is more expensive for the tusks and you won't use up your scrap wood using dowel. Aesthetically it may not be as appealing. Since the mortise is straight, the shelf sides at an angle of 8˚ and 2" thick, the shelf/tenon being 2" thick (approximately) you'd need a mortise 5" wide vertically to get the tenon through (if my math is correct). This giant gap could be covered up by creating a tusk shaped appropriately, ie. not a dowel tusk. There's certainly an aesthetic sacrifice to doing it this way.
I think this was merely a demonstration of the sheer ruggedness of the mug rather than any practical purpose.