Actually, many claims have been made that Sky is clean.
Anyhow, did you seriously compare Hesjedal's Giro win to Froome's rise in the coming out of nowhere stakes? I underrated Hesjedal because he has quietly accumulated his palmarès, but to compare his ascent to Froome's meteoric rise is insulting to the Canadian in extremis.
Hesjedal's been accumulating top 10s in stage races for a few years now, from 4th in Catalunya back in 2006 to 8th in Tirreno 2008, won a mountain stage of the Vuelta in 2009, and while 2010 was a surprising breakout, he prepared for that unexpected 7th in the Tour by coming 6th at Catalunya and 5th at California, and was picking up top 10s in hilly Classics and other one-day races all year. 2011 might have been disappointing but he still managed top 10s in País Vasco and California. While you may be suspicious of his late-career development (almost all of his best results have come from 29 onwards, like Wiggins), this Giro win was the culmination of three and a half years of building results.
Froome was not. Ryder Hesjedal wasn't about to lose his contract when he turned into Ryder the GT winner, he was a guy with several years of bankable results. Froome was a guy who had shown a bit of promise three years previous, but for a variety of reasons had neither capitalised on it nor shown progress, and in fact his CQ scores and race results were going in the opposite direction, until suddenly, abracadabra, he's losing GTs only because of a) bonus seconds, and b) his team not allowing him to ride his own race.
Santiago Pérez finished 4th in Romandie '02, 6th in the Setmana Catalana '03, 7th in Aragón '04 and 7th in a Tour de Suisse mountain stage as preparation for his breakout at the '04 Vuelta. Bernhard Kohl was 7th in the Österreich-Rundfahrt '05, 5th in '06, 3rd in the '06 Dauphiné and 6th in the '08 Bayern-Rundfahrt before he 'came out of nowhere' in the 2008 Tour as if a rider who's been on the podium at the Dauphiné can be considered a scrub the way Froome was prior to the 2011 Vuelta. Ezequiel Mosquera finished 7th in the Volta a Portugal back in '04, moved to Kaiku for '05 where he was top 10 of the Ruta del Sol, Vuelta a Murcía, Volta a Catalunya and Vuelta a Burgos, and won a stage of the Vuelta a la Rioja. He followed that up in '06 with another top 10 at Burgos and one in the Giro del Trentino before his breakout at the 2007 Vuelta.
Those are three of the biggest 'out of nowhere' transformations of the last ten years, and they all had a better palmarès than Chris Froome before their breakout tour, and they all ended the same way. Ryder Hesjedal doesn't belong on that list.