Just for reference sake the fungal projectile is not like the projectile seen on youtube it is much faster, so fast that many players do not remember it as a projectile, it will only give about an extra quarter of a second or less time to move but it does mean that you have to aim a little bit more.
The youtube links I posted:
These Are in fact the PTR fungal growth projectiles, they were videos that were taken and were posted on TeamLiquid the last time during the last PTR in which Blizzard rebalanced the infestor.
Blizzard has rebalanced, or has attempted to rebalance, the infestor many times. The fungal growth becoming a projectile was widely regarded as a mistake that should not go through and thus did not.
It was worth investigating on the PTR, which blizzard did. It didn't work as a projectile and they've tried it out as one several times already.
People just have a very short term memory when it comes to the PTR. It might be no one actually goes on it when they put up tests. However the uproar over reverting the Fungal Growth projectile on the PTR was quite loud so it is very hard to forget.
As far as Fungal Growth being drastically changed to be unable to decloak Dark Templar and Ghosts, that is a direct Nerf to Zerg's already lacking defensiveness which means that this change wouldn't be seen until HOTS where Zerg theoretically should be able to defend itself better and not need infestors as much as they do now.
Infestors are unfortunately the support caster(ala sentry) and combat caster(ala high templar) for the zerg. Which is why they are so extremely important and extremely hard to balance.
Fungal growth is extremely important in Zerg survival in the late early to mid game when they are the most weakest similar to Force Field.
Now imagine trying to balance High Templar but being forced to nerf sentries in the process. To nerf Psi-Storm you end up having to nerf force field... Ugh.
People really should give the balance team more credit for this mess they have to figure out. This isn't easy and the infestor is such an important unit for Zerg survival in all match-ups, imagine how difficult this is.
Try to take yourself out of your own personal bias for your own favorite race and try to figure out how to untangle this mess they have gotten themselves into with the infestor.
As said many times before, the Infestor is a band-aid that is there to cover up for many of the flaws left in the game at release. It is a band-aid that is covering a now festering wound and it is time to clean that wound...