They certainly do and deserve credit for not completely screwing them up. But besides keeping them running, has Google really done much to further either success? Blogger has remained pretty stagnate for the last few years. Would anyone here (looking for a hosted blogging platform, to keep things fair) choose Blogger for their blog today? Google has paid the bills for Youtube, granted (anyone know if Youtube is turning a profit yet?), but Youtube's success seems more attributable to its early-branding rather than any Google help.
Just to take a small example with youtube, they've created an entirely new ad platform. Building out an ad platform at that scale is by no means easy - there's an ad server, BT, targeting, reporting, payments to youtube publishers, not to mention recruiting a sales team. And that's just one aspect of youtube that google's had a hand in.
