The issue, as I see it, is these sites are all companies with hired workforces. In other words, at WU, at Twitter, at Facebook, at weather.com, etc., there are people who draw paychecks whose job it is to "develop" the appearance and functionality of their sites. They get PAID to make changes. So, imagine a site comes along and is universally hailed as the greatest thing since paper towels. The best thing to do might be to just leave it alone! Let it build its following and reputation. That sounds like a great strategy. But the problem is, the department that works on the technical side of such a site can't justify the retention of their services to the site's owners if they back a plan calling for no significant functional/appearance changes in favor of a focus on simple housekeeping & maintenance. Giving websites periodic makeovers is what puts food on the table for more folks than you can imagine. The downside is many of these changes are, at best, unwarranted, and at worse, can ruin a once good website.