In the core SCBG , the zerg had 3 module slots, while each of the protoss and terran had 5. This was due to the obvious fact that zerg don't build supply modules, as they use each new type of building to increase their build limit by 2, due to their "creep" racial ability. This meant that if all the players had the same number of non-supply modules (eg. 1 air defence and 2 R&D, or 3 R&D), then the protoss and terran would only have 2 spaces left to build supply modules, each providing 1 build limit, giving them a total of 4 build limit, compared to the zerg 6 build limit, if they have the 3 different buildings built. I suppose this was meant to translate the fact the superior units building capability of the zerg as in the video game, and also point out the fact that the zerg rely more on numbers than on shear power. This is acceptable in a way, although i'm not really sure this is really balanced in end-game, as I can see that end game units don't have that much difference in power gap between zerg and portoss/terran. I still haven't got to many end-games to decide that yet.
The issue I am discussing here, however, are the slots in the expansion. Let me first point out the fact that there were 3 new types of modules introduces in the expansion, beside the old 3. This led to the fact that the module slots had to be increased. The surprising thing here is that the terran and protoss' slots were increased by 1 each, giving a total of 6 slots each. But the zerg were increased by 2, giving them a total of 5!
This means that if we address balance issues, then in order for a protoss or a terran player to be on the same level of modules as a zerg player, they would be forced to have only 1 more space for building a supply module. This leaves them with 3 build limit, while the zerg is still at his easily achieved 6.
While I haven't played the expansion a lot, simple math calculations make this look very unbalanced, due to the fact i pointed out earlier ot the similarity in end-game units' power. For example, if a protoss player has the same number and types of modules as a zerg player, and has a supply module (which he will have to spend 1 more build order to build beside his other modules), then he ends up with a build limit of 3, making him capable of either building 1 archon, or 3 carriers. The zerg player on the other hand, who has easily achieved 6 build limit by building a queen's nest and an upgraded spire, can use his build order to build 3 guardians, or he can choose to build 3 ultralisks and 3 devourers. I don't think there is a need to point out which is stronger and by what scale!
What are your thoughts about this guys?