As a 20+ year computer programmer, and one who has become intimate with the old links code (2.0, 1.11) and has started to look and work through the SQL 2.0 code, what happened, is the project got away from them.
It looked like a simple upgrade.
Then they added a feature, and 6 new "problems" or changes became apparant, and it was worth fixing them before the release. Then, in doing so, new "problems" became apparant, and the whole thing turned into a complete rewrite of all the core modules, all the core logic, and all the code on top of the logic.
If you go through the new code, you'll not recognize anything.
So, think of this as going from version 1.2, to 1.3 to 1.5 to 1.6 to 2.0 without ever releasing the intermediate versions, and all the hassles of support, upgrades, and stuff they'd have to go through.
So, while from a user stand point it looks like just delays, they chose not to release intermediate versions, going instead for a full version release, and _one_ upgrade process, rather than 6 or 7 upgrade processes.
http://www.postcards.com FAQ:
http://www.postcards.com/FAQ/LinkSQL/