My biggest questions are as follows...
Why not field one Crusader Squad in a DP in your large list? IT seems to me the 8I 2N squad would benefit greatly from the mobility of a drop pod.
What is the justification for not fielding a LS with HB and AC? I have used that config in nearly every game thus far and the mobility has allowed me more than one objective won while still kicking through side and rear armor.
Also, why the lack of love for Assault Squad? I have found them nearly invaluable in my Codex list and the Vows combined with a Marshal on the board would make them extremely durable. (With Codex Marines Ill include a Chaplain w/JP to get those re-roles and Power weapon)
I will wholly admit my lack of experience, but these are my thoughts. I look forward to your feedback and am very excited to build my BT list.
I was going reply sooner, but then the new BT FAQ hit so I've been distracted with that the past week or so. Anyway, on to your questions!
1) The mobility gained from the drop pods are a one time use thing. Once they land, the unit loses whatever mobility they had gained. This can potentially leave them out in the open or away from the action if your opponent is maneuverable enough. Generally speaking, unless they have ranged weaponry that is relentless (dreadnoughts, terminators), it isn't worth bringing in a couple of drop pods to the list. It really is go all out or nothing. Rhino's are much better suited to providing mobility as they can both provide protection for an embarked unit or redeploy if necessary.
2) I don't take the HB/AC Land Speeder because its too expensive for what it does. It's primary goal is to take out infantry and if its lucky, it can knock out vehicles if you get some side/back armor shots as you mentioned. However, the MM/HF Land Speeder kills vehicles well from any armor face and armor value and the Heavy Flamer is excellent at destroying mobs of infantry. Alternatively, the newly buffed Typhoon-Pattern Land Speeder can lay down loads of AT fire support from long ranges and has enough firepower to hurt infantry as well if needed. All while at a very safe distance from your opponent. I prefer efficiency in my Land Speeders and the ones I listed do it better in my opinion, and they are cheaper points wise. :)
3) I dislike Assault Squads because they are not durable and don't provide the fire support a Land Speeder can, for much less points. A basic 5-man Assault Squad with dual-plasma pistols, MB, and Powerfist is rocking 145 points. That's two Land Speeder Typhoons. In addition, they really aren't all that strong in close combat, even with an attached IC. A normal Crusader squad is just as strong, but for less points and is scoring. On top of that, Assault Squads are extremely vulnerable to shooting of any kind and 3+ saves will not save the unit for long against focused firepower (which is what they will receive). If they were cheaper points wise and had more options available to them (like what the Blood Angels have), they would be an option for me. Until that point, I believe Land Speeders fill a much needed hole in our lists.
So hopefully that gives you a little bit of insight on my decision making process and answers your questions. If you feel that I inadequately addressed them, just let me know and I'll try to explain it better. And of course, feel free to message me if you have any further questions. Good luck with your army!