My simple view on the Nuclear Suppliers Group and the Indo-US nuclear agreement: First, the entire agreement is premised on the NSG community accepting that India is a de facto, not de jure nuclear weapons state. In other words 1) India has not and will not sign the Nuclear Non-Proliferation Treaty, and 2) that it has demonstrated that it possesses nuclear weapons and intends to retain them. The challenge for the NSG is to skirt these two issues in a manner that enables nuclear trade with India and also ensures that nothing in the process goes against their non-proliferation commitments. As of now they seem unable to do so.
You may say that India is demanding to have its cake and eat it too. Possibly, but that is what the so-called Nuclear Weapons States under the NPT do. India has stayed out of the NPT and has broken no international agreement in testing or possessing nuclear weapons. The 123 Agreement between India and the US has successfully dealt with the issue, as has the India-specific IAEA agreement by the simple device of working on the agreement in the narrow sense—dealing with nuclear trade issues rather than the larger question of nuclear weapons possession by India.
The NSG purists however want to get in through the backdoor what was kept out of the front.
For a more detailed analysis, you must see Siddharth Varadajan in The Hindu