[bluGill]

Construction generally is not doing a brand new greenfield project. Experienced web developers can put together another website for pretty close to budget. As soon as you deviate from the framework and tools that the experienced web developer knows well though estimates go out the window.

Big construction projects have a lot of well understood parts. Sometimes you get unexpected rocks or something, but for the most some countries have done much better than others at controlling costs in projects of similar complexity which suggests that the difference isn't because it is hard to estimate.