The IIHF agreed through 2014 that any tournaments played in North America will be played on NHL-sized rinks. This has applied to the 2008/09, 2009/10, and subsequent 2010/11 WJC (U-20) and the Olympics. This was not done last-minute...it was negotiated years ago.
The IOC does not bear the construction cost for new facilities...the host city/country do. It would have involved doing a temporary retrofit of GM Place (christened Canada Hockey Place for the Olympics) and (importantly) eliminating several hundred prime seats. Given that Montreal 1976 was a financial disaster and Calgary 1988 marginally better, not having to spend billions of Canadian taxpayer dollars (mine for one) on new facilities...sounds like a brilliant idea. They did build infrastructure (new highway to Whistler, new airport road into downtown, etc.) but that will continue to benefit the city and visitors.
According to FIFA there are no specific sizes for football pitches other than minimum widths, so yes, Brazil could have a slightly wider than minimum pitch if they wanted.