Most of my worldbuilding blogs revolve around me filling in details, pointing out things I find interesting, and so forth. This one's a bit different as I don't have an answer for it. It's a question that I would be curious to see the writers answer, but I doubt they'll address it (accidentally or otherwise).
We'll start off with what we know:
Pegasi can walk on clouds, and manipulate them like they are solid objects. Other pony tribes cannot, and it has been demonstrated that non-pegasi ponies just fall through clouds except in extreme cases when the cloud is 'compressed' deliberately (Rainbow Dash doing a special maneuver to save the rest of the Mane 6 when they fall during one of the Wonderbolt Cadet episodes, etc.), or the pony (and dragon which will become important later) are enchanted by a special spell by Twilight (or any other accomplished magic-user with a similar spell, I assume.) It is implied that this is part of the pegasi 'magic' that also allows them to fly despite their wings not actually being big enough to support themselves in flight. This is the magic that Tirek drained from them during that particular episode, rendering pegasi grounded.
Scootaloo, despite being a pegasus who cannot fly *is* able to cloudwalk. She has difficulty reaching Cloudsdale, but once there has no issues walking around. So however this magic is expressed, it's not fully linked with the ability to fly. A bit of a contradiction of the previous implication, but okay, it was just an implication after all, not a stated fact.
Luna showed that alicorns, being creatures that have the potential abilities of Unicorns, Pegasi, and Earth Ponies, also have the ability to cloudwalk as she laid upon a stormcloud and startled Rainbow Dash with it at one point as a prank.
Gryphons can also do this, as demonstrated by Gilda in her first episode lounging around on a cloud while interacting with Rainbow Dash. This is where things start to go off the rails a bit. It makes sense for her to be able to do so for plot reasons, as it allows her and RD to go somewhere and 'chillaxe' that takes considerable effort for Pinkie Pie to deal with. However, for worldbuilding purposes, it throws a wrench into things. This is now not an ability unique to pegasi, but other winged creatures seem to have this ability as well. It's not tied to pony-kind's innate magic. Just as a side-note, Gryphon wings are also drawn considerably bigger in ratio to their bodies than pegasi wings, so likely they don't need as much magic to bypass the laws for aerodynamics.
But, okay, Pegasi and Gryphons can cloud walk. Fine, no problem.
Here's where it breaks down for me: Spike can't cloudwalk. He falls through clouds, just like any non-pegasi/gryphon. At least, that's what happened before he got wings...
So these are the questions that bother me: Can winged dragons manipulate clouds the same way pegasi and gryphons can? Is this ability connected to the physical presence of wings, but not necessarily functional ones? When Tirek drained the pegasi ability to fly, did they also lose the ability to cloudwalk? Could Tirek have drained this ability from gryphons? The wings on Spike (and other teenage-type dragons) are even smaller in ratio to their bodies than pegasi, so their flight ability is definitely magical. Would that have been drainable as well?
My opinion, with no basis in any evidence whatsoever, is that Spike should have had the ability to cloudwalk from the beginning. It should have been a very brief moment of confusion when he did it for the first time, with a comment of 'How does that work?' followed by 'It must be a dragon thing. We'll get back to it, we've got bigger things to deal with right now.' and then just leave it at that, open ended. However, this is all in retrospect, and there's no way the writers at the time were even vaguely concerned with this kind of worldbuilding.
That's what we're here for, afterall.
As another side-note: It would have amused me to see the Cutie-Mark Crusaders walking through deep-ish snow drifts at some point, with Applebloom breaking trail for Sweetie Bell, while Scootaloo simply walks on top of the drifts. Just to point out some differences in how the different pony tribes deal with things naturally, and as a toss-away reference to a specific scene in the Lord of the Rings novels where the humans break trail for the hobbits, and Legolas just walks on top of the snow.