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I've never heard of being able to buy a 1 year subscription to VS 2010 Pro before. Are you sure that it wasn't a 1 year subscription to MSDN that you bought as an adjunct to VS?
If so, then you could keep on using VS 2010 Pro 'for ever' but your MSDN subscription would cease after 1 year and so you'd no longer get any updates.
I also wasn't clear how purchasing VS 2010 enabled you to acquire VS 2008 at the same time?