What do icons on the tags mean?
Android has a logo, IOS doesn't.
Are tag logos even a good idea, seeing as the low number of logos?
The logos that you do see are there because someone (normally the company behind the technology) sponsored them.
iOS doesn't have a logo because Apple didn't sponsor a logo. Android does because (I assume) Google did.
Having a large number of tag logos would in my opinion be a bad thing - it would clutter the UI and distract from the actual tags and questions.
Having a low number does draw attention to those specific questions - precisely what they are designed to do.