EPTTvZ:
BW Early Game:
Terran SCVs can actually scout fairly "safely" provided he has good juking micro even with 4 lings out on the field. It's possible to do very quick turns to prevent ANY SCV damage - allowing you to scout quite extensively. Most of the time, you can determine if the zerg is going 2hatch muta or lurker contain, etc. without resorting to excessive scans. (Allowing ebay before academy builds to work out).
In SC2, the instant 2 lings pop-out, your SCV can't even juke off-creep, and if it goes on creep, it will die extremely fast
BW Mid Game:
Because there are no Xel'naga towers, it is actually possible to send out a drone/probe/SCV into the mid field without it being instantly killed. Xel'naga towers means that the player with the more mobile army has almost complete control of the map, simply by camping a ling or hellion at a tower. During this time, it is almost impossible to scout CHEAPLY (without scans, overlords, observers, etc.)
In SC2: Scans don't guarantee that you'll be able to find the tech. Smart zerg players hide spires with an overlord pooping creep in sometimes the most absurd locations.
TvP:
Early Game:
BW: Again, goons AI in BW was just lolol, you can easily scout out the early tech path the toss is going.
Where as in SC2, the instant a stalker from a single gateway is out, you won't have a clue if toss is going 4gate, 3gate vr, 3gate robo, or 2 gate robo expand. It literally becomes a roulette.
Mid-Game:
BW: Its fairly easy to ninja an SCV or a vulture into enemy bases, again, because there are no xel'naga towers. Furthermore, vultures usually allowed you to determine the tech path that the protoss is going.
SC2: The presence of Xel'naga towers often means the protoss can quite easily shutdown hellion raids by camping 2-3 stalkers at each xel'naga tower.
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I think ZvT/ZvP/PvT, and even the mirror matches, has similar issues when it comes to scouting.
Essentially, Xel'naga towers makes map control COMPLETELY lobsided. It makes it so the player that doesn't have control of the xel'naga towers has very little ways to scout CHEAPLY.
I think by removing the xel'naga towers, we'd actually be able to have more consistent games because it would allow BOTH players to having equal scouting opportunity. Currently, xel'naga towers severely punishes the less mobile player.
I think the above elements are often what leads to "Build-order wins" that we see over and over again, even at the highest levels because it can be so incredibly difficult to determine the builds a player is doing.
