US caving in to Iranian diplomacy

The much-awaited nuclear talks between the US+5 Great powers and Iran have concluded without any breakthrough in Geneva. However what is of interest is the fact that the United States has decided to completely revise its policy vis-à-vis the Iranian nuclear programme. What has been the reason for this complete 180 degree turn by the US? Is it the fact that the US has realised that it has failed in Iraq and Afghanistan and cannot afford to open another front with Iran? Or is it the fact that Iran due to its perseverance has finally brought the US down on its knees? Should a nuclear power like Pakistan learn a lesson from Iranian counterparts?
The White House had previously reiterated that it wouldn't be involved in any pre-negotiations with Tehran unless it gave up uranium enrichment. So, why has the US made a shift in its policy towards Iran now? Some within the Bush Administration are for diplomacy but term reversal in the policy as Diplomatic Malpractice. By agreeing to suspend its demand for cessation of uranium enrichment, Washington is signalling to Tehran that it need not adhere to the current United Nations Security Council resolutions. So, rather than reinforcing diplomacy the US has shown that its threats were empty.
Recently, Iran has announced that it now possesses 6,000 centrifuges, a significant increase in the number from earlier 3,000 centrifuges as previously said in its uranium enrichment plant in Natanz. This announcement is yet another act of defiance by Iran in the face of demands by the US and other great powers for Tehran to halt its enrichment programme. However, Iran has stated that the US and the other great powers have tempered their demands, asking it not to freeze enrichment but rather not to expand its current programme beyond 6,000 centrifuges. So, the US and the others have no problem as long as the programme is not expanded.
It must be remembered that uranium can be used as nuclear reactor fuel or as the core for atomic warheads, depending on the degree of enrichment. The workhorse of Iran's enrichment programme was the P-1 centrifuge, which was run in cascades of 164 machines. But this year in February the Iranian officials confirmed that they had started using the IR-2 centrifuge that can churn out enriched uranium at more than double the rate. Tensions increased further when in July, this year, Iran test-fired missiles in the Gulf, including one it says could reach the Jewish State and the US bases in the Middle East.