This isn't true. Labour's manifesto [pdf] pledged a referendum on AV on the basis that the system will "ensure that every MP is supported by the majority of their constituents voting at each election".
Press a No2AV supporter on this and they'll explain that they meant to say is that it wasn't in either of the Coalition partners' manifestos.
This is true. The Conservatives have long advocated keeping the current First Past The Post system, whereas the Liberal Democrats have long campaigned for a move to the proportional Single Transferable Vote system.
These two systems have two key distinctions:
• FPTP takes place in single member constituencies, where one MP is elected to represent all the people in the area. STV would have multi-member constituencies, where multiple MPs would be elected that would represent a wider variety of views of people over a bigger area.
• FPTP requires the voter to mark their ballot for one candidate only, and the most votes wins. STV allows the voter to rank several candidates in order of preference so that the winners have a bigger consensus.
AV shares features of both FPTP and STV - it has the single winner feature of FPTP and the preferential ballots feature of STV. While AV is not seen as the perfect system for the Tories or the Lib Dems, it has features which both parties like.
Yes, this does make AV a