I don't think India needs a fourth fast bowler. Ishant and Bhuvi are workhorses - Bhuvi bowls within himself and Ishant is built for long spells. Shami is the only quick now who can't bowl a lot of overs each innings. If India stick with picking 2 workhorses (guys like Pankaj and Vinay Kumar fit that role too) and one express bowler (Aaron, Yadav and maybe Pandey too), they can comfortably rotate using 3 quicks. Especially if they play 2 spinners.
Jadeja has shown he can bowl tightly in all conditions, and with the newish ball, and then you have Ashwin as the main strike weapon when the pitch is wearing. So even in conditions favourable to seam bowling (like Lords was), they can get away with 3 quicks, 2 spinners, and maybe some Virat Kohli to fill in. You just have Ashwin bowl a bit less. And then on flat roads, Ashwin and Jadeja can bowl the bulk of the overs (which tbh isn't a bad thing as they're both pretty good) and let the quicks operate in bursts. And then on pitches helping spin, well you have 2 spinners to do all the work with the support of part-timers like Vijay/Rohit/Dhawan.
This balance works especially well because Jadeja, Ashwin and Bhuvi are all pretty solid batsmen, so we don't play a long tail and we get 5 bowlers.
If India were to pick a 4th seamer it wouldn't really enhance the quality of the attack in anyway - as promising as Aaron and Yadav are, they are still very raw, and the other quicks are hardly going to turn in better figures than Jadeja even in seamer friendly conditions. And then if you go looking for a medium pace bowling allrounder, you have Binny, Irfan Pathan, Rishi Dhawan or Nayar. And are any of them going to do better than Ashwin and Jadeja? With bat and ball? And in the field? I don't think so.
3 seamers 2 spinners also gives that flexibility for a pitch like Lords was, which seams and swings initially and then takes turn later.
