You can't stress too much that analogy. The property in question is a pile of fungible STEEM, not a specific land lot, and Ned had been already selling part of it those last years to fund expenses.
I would say that Ned had been selling parcels in one place to fund the building of the Steem condominium in some different place. Now Justin has come and bought the remaining parcels, but not differently that the other smaller investors before him.
Ned is still bound by his promises and must dedicate the proceeds of the sale to the Steem condominium. The encumbrance did not transfer to Justin, in the same way as it did not transfer to the other investors when they bought a parcel.
obligations are obligations, regardless of who they obligate and what they are obligations on. This is a clear principle at law.