I suppose view-through conversion might be clicking on ad, user goes to site, completes purchase and then some kind of callback gets fired. On the other hand, Google analytics one would be user completes purchase, GA looks at which referrer came last and registers that as the source of conversion?
Google Analytics conversions are last touch click through conversions, where all marketing touches compete and the last that occured gets 100% of the credit.
The ubiquity of Google Analytics and thus, ubiquity of "last touch" conversion tracking, has really helped Google make the case for Adwords. If someone sees an ad from a display advertising company, retarteted or otherwise, it's not uncommon for them to head to Google to look up more information about that product or service. If they then sign up or convert, the advertiser will see Google analytics listed as the sole source of the conversion. This is great for Google and less great for everyone else higher up in the funnel.