This is how Roman Kreuziger works all year for a GT.
2010:
1st, Giro di Sardegna (+stage win)
3rd, Paris-Nice
8th, Volta a Catalunya
16th, Tour de Suisse
9th, Tour de France
27th, Vuelta a España
2009:
9th, Vuelta al País Vasco
1st, Tour de Romandie
3rd, Tour de Suisse
9th, Tour de France
2008:
2nd, Tour de Romandie
10th, Tour de Luxembourg
1st, Tour de Suisse
12th, Tour de France
That's working hard and performing in a range of top events from March to September there.
Wiggins, by contrast, prepared for the 2010 Tour by coming 3rd in the Vuelta a Murcía, and soft-pedalling everything else except the Giro prologue.
Rogers is somewhat better at racing all year round (his preparation for the 2010 Tour involved winning the Ruta del Sol and the Tour of California, 6th at Tirreno-Adriatico and 2nd in the Criterium International) but isn't as much of a GC threat as Kreuziger.
Gerdemann is a bit of a misnomer as a comparison; like Evans Gerdemann has the tendency to get excitable and try and win anywhere he can, which means he doesn't tend to save himself for a GT at all. With Gerdemann however, it's more endearing than with Evans because Gerdemann isn't going to win a GT so you don't mind him expending energy. He had a bad Tour because he got into the infamous L'Aquila break and broke his back trying to defend a top 10 position in the Giro.
Apart from Wiggins I can't really see anybody there who you could really describe as only trying for GTs - and even then that's with Wiggins only having the one year's experience of GT-hunting.