No, because it is still perfectly possible to grow giant mushrooms outside in plain day by placing 5 dirt blocks:
I just tried this in 1.2.5, and the 5 dirt blocks doesn't work any more. If I extended the pattern out one extra block though in each direction (and filled in some spots in the "cross" to make a disc instead above the center spot) I was able to get the giant mushrooms to grow with bonemeal.
An interesting "solution", and it is interesting this became a "bug fix" as I had been growing these before in 1.2.3 without the cover.
So, right now we can still grow mushrooms outside , but one must be annoyed by making a cover for said mushroom to grow, so it's actually not prevented, but annoyingly possible to be done.
This looks like that day when Mojang made Zombies smash the door, and it didn't add any real difficulty to the game, just annoyance, forcing the players to make block-doors instead of regular wooden doors.
Then I guess by game logic, all giant mushrooms should explode into 50 tiny shrooms when the sun comes up.
True, although it should be pointed out that growing giant mushrooms in Mycellium still works in daylight with light levels at 15 that won't grow on ordinary dirt even with the changes being discussed here. I suppose that makes Mycellium even more precious? Silk Touch still allows you to harvest Mycellium as blocks you can put in your inventory, so if you want an "instant house", you need to bring along some Mycellium along with your mushrooms and bone meal if you also don't want to mess around with the upper "protective roof" to cover ordinary dirt to grow these items.
In 1.2.4 onwards, giant mushrooms have been effectively removed. It is now no longer possible to plant a mushroom anywhere outside, even at night, rendering it impossible to bonemeal. It is possible to use a glitch to get them to plant outside, but that doesn't change the fact that there is no longer a vanilla way to do this. Is anyone else as bummed as I am?
I noticed this, but I found a solution! Plant your mushrooms in the Nether, but not next to fire or lava, then just bonemeal it
You can still bonemeal mushrooms basically anywhere but however....... In vanilla (atleast in my case) you can no longer get giant mushroom blocks (stems, polka dot, or brown) anymore since around 1.5 . Now you can only get spore blocks