(a) Are they obligated to handle anything that they would handle over the phone via a letter too? I don't feel like many companies would be willing to do this.

(b) What if they just do all the typical customer service BS on the phone over snail mail? People spend hours or even days with a lot of back-and-forth to get non-routine stuff sorted out... if you do that over snail mail it could easily take many months to do things right. Not exactly practical, especially when you have a deadline coming up and it passes during this back-and-forth mailing.

I guess the answer is in many ways contained in the blog post.

Is there any legal regulation or contract compelling them to respond to you? If so, use that as leverage. If there is not, you may not be able to compel them to do what you want.