Why are images blocked in email campaigns in Gmail only?

Does anyone no why the images keep getting blocked in gmail and not my other yahoo of aol or ms email testing accounts. gmail no longer even offers an obvious setting to always display images… gmail is getting pretty lame these days…

According to Google, whether you have image filter on or off, all images go through, “Google’s image proxy servers and are transcoded before they’re delivered”

I doubt other web based email clients have that extra level of precaution. They probably just give you a blanket option to block or not block by default