Response from Riot Pwyff to a similar question:
[{quoted}](name=Riot Pwyff,realm=NA,application-id=A7LBtoKc,discussion-id=IE6vEmv6,comment-id=0003000000000000,timestamp=2015-11-14T01:53:47.502+0000)
Because I just sent out an email on this: Removing true sight was a deliberate decision because, ultimately, stealth champions have their power budget allocated to being difficult to detect. Giving 'standardized' counters that everyone gets for free means the champion's just kind of... not stealthed after a certain period of time. With the trinket changes, sweeper still detects bodies and we want to see a world where a stealth champion's 'power' of stealth comes with the ability to conceal their health. If player adjustment is a hard - "we must buy pink wards" - to the point where it becomes mandatory to play against stealth champions, we'll fix accordingly. But if players understand this and know how to work with sweepers, maybe we won't need to.
full thread: http://boards.na.leagueoflegends.com/en/c/developer-corner/IE6vEmv6-taking-a-break-this-friday-join-us-for-a-hows-preseason-tracking-qa-on-tuesday-11172015?comment=000300000001000000020000