|WikiProject Chess||(Rated Start-class, Mid-importance)|
Rxd8 is indeed crushing for Black -- it threatens Rh8# in one more move, failing Ng7 and possibly a subsequent Bxg7 and Kxg7. White's material disadvantage is gone and black is on the defensive; White can withdraw the offered knight after Black addresses the mate threat (and maybe completes the exchange on g7).
The alternative is no better -- R2xd5, a8=Q turns White's four point disadvantage into a one point advantage in material, and with a queen and rook versus two rooks, likely leads to a slightly slower checkmate.
This part seems to be wrong: "However, with 2...Rxb8, White can not play 3.Qxb8 because this would lead to 3...Ra5#."
This would be true if white knight was still at b4, blocking the king - but the knight has moved, so white king can move to b4 after Ra5+.
The text says "If Black plays either 1...cxd6 or 1...Bxd6, White will capture Black's queen. Therefore Black has no better play than 1...Rxd6 2.exd6 Qxe2 3. Rxe2 Bxd6, conceding the exchange for a pawn." This is wrong, because black cannot move Queen to e2!