View through conversions are conversions that take place after a visitor has just viewed an ad and not necessarily clicked on the ad. In the case of traditional display, the ad may not have even been visible on the screen it was just served somewhere on the page.
Google Analytics conversions are last touch click through conversions, where all marketing touches compete and the last that occured gets 100% of the credit.
Yep. And just going by Google analytics tracking is a rough way to assess marketing channels, agreed.
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.