It seems to me that your approach is making some assumptions about how the data is distributed that aren't necessarily guaranteed to hold in practice, and a tree has a chance of being robust to at least some of those. For example, whatever random hyperplane you choose has to be informed by your data. Suppose you make a particularly bad choice for one of those hyperplanes, with your approach you'll be stuck with that for all time and have a bit in your hash that's biased to heck, but in the tree approach you only suffer when you hash your way down to the lousy node, and all other paths will be unaffected.
It seems to me that your approach is making some assumptions about how the data is distributed that aren't necessarily guaranteed to hold in practice, and a tree has a chance of being robust to at least some of those. For example, whatever random hyperplane you choose has to be informed by your data. Suppose you make a particularly bad choice for one of those hyperplanes, with your approach you'll be stuck with that for all time and have a bit in your hash that's biased to heck, but in the tree approach you only suffer when you hash your way down to the lousy node, and all other paths will be unaffected.