It's surprising that wasn't being done in the first place. I used the Warcraft 3 map editor, and it was simple to include references to attribute values in an object's description. Don't know why the DotA2 team didn't port that feature over when moving to the new engine.
This is a good example of a general rule of thumb I learned, if you need to do something once or twice do it by hand, but if you do something three or more times make it a function! Looks like Dota 2 updated their spells a few more than 3 times ;)
Interestingly, this has been a big point of discussion in the Dota 2 playerbase. Dota 2 is one of the most complex games ever created and it rapidly changes on the order of days or weeks. At one point, the in-game descriptions of spells were months or years out of date because they were being updated manually. After much hue and cry from the community, the developers finally made the tooltips get generated from the same code that determined the spells' effects. Things are a bit better now.
There is still a quite a bit of ways to go though, in terms of generating documentation for all the other mechanics in the game, which are crucial for gaining competency in the game, but which are only available due to third-party community efforts (often via people reading the game's codebase to understand subtleties), instead of being available inside the game.