If the initial load-up time is slow, then you're probably less likely to click that Twitter link knowing that the initial page-load is always slow.
The warm-cache situation only matters to people that are on Twitter all the time, so this possibly has the effect of keeping existing users happy while raising a barrier to new users (or pushing infrequent users to completely abandon the system).
Secondly, you're only looking at download size (the importance of is really to imply a certain amount of time it takes to download those resources). Since Twitter's JS platform is about doing all of the HTML rendering on the client-side that has to be taken into account (this wasn't a concern in the past when it was mostly done on the server-side). If the page takes 3s ~ 5s to load even with a warm cache and a tiny (size) ajax-request, then it sort of defeats the purpose (unless your purpose is to relieve server-load instead of in-browser load times).
The warm-cache situation only matters to people that are on Twitter all the time, so this possibly has the effect of keeping existing users happy while raising a barrier to new users (or pushing infrequent users to completely abandon the system).
Secondly, you're only looking at download size (the importance of is really to imply a certain amount of time it takes to download those resources). Since Twitter's JS platform is about doing all of the HTML rendering on the client-side that has to be taken into account (this wasn't a concern in the past when it was mostly done on the server-side). If the page takes 3s ~ 5s to load even with a warm cache and a tiny (size) ajax-request, then it sort of defeats the purpose (unless your purpose is to relieve server-load instead of in-browser load times).