Truth be told lots of things about demigod are badly designed, this comes from releasing the game well before it was ready (proof: all the networking problems on release).

One of the reason's cataract is played so much is the length of the game's can become excrutiatingly long on bigger maps, and the fact that online play breaks down and starts to severely lag with more then 6 players.  The networking in demigod is atrocious so people tend to play cataract.  On larger maps lag can be a huge issue, Zikurat is one map where you can experience severe lag.

I personally blame the developers for having so few good maps and not play testing the game enough.  I agree there is nowhere near enough map variety in demigod.

First of all I would like to say I have a bias opinion about Cataract because I love it.

The portal issue you speak of gives the map a character that the others do not have. The other maps do not focus on portal capture and cataract does, now to me that is diversity in map structure not limitiation. So my answer to your question is that the lack of archer towers was an intentional map design to provide variety in map structure, not a mistake.

I have also won many games by pushing the middle lane and perma locking the valor flag infront of the citadel on cataract. This allows you to go and heal, comeback with a freshload of giants, and do some more damage to that citadel. Winning this way almost always requires giants though.

Yeah, I sort of think Leviathan is boring compared to Cataract because of the portal cap element.

I believe you get a reward for every wave of allied creeps that spawns from your enemy's portal. Not sure, but it's DEFINITELY not worth dying for. (unless you have maxed out giants)

Good point, I would say it's best to capture portal flags whenever possible when the risk of dying is low. The badly defended portal flags make cataract much more fun.

I doubt it's intentional. I was played a game with frogboy and was trying to get him to help push a portal early, I think at war rank 4 or so, and told him that it was worth it because it would give the whole team gold and exp. His reply was that he knew how it worked because he designed the mechanic, and in spite of that he still didn't seem to value the portal all that much. So to me it seems unlikely that the intent was to make the whole game into a flag lock struggle before rank 10, but who knows?

Maybe Frogboy himself can shed some light on it. Basically right now capping that port shuts off creep waves and lets your creeps demolish the front of their base while they fight for the port, it gives you a gold mine, and it gives the whole team some gold and exp as the waves come out.

You can lock one and then port to help out ina 3v3 across the map and still get exp off that lane while you're away. Cow is right that it's specific to Cataract, but I would say it's a problem specific to cat rather than a feature. Regardless if people would just stop playing cat over and over again it wouldn't be such a problem.