US-ASCII characters versus XML characters ... why such a huge discrepancy?

Hi Folks,

Below is a table that shows the US-ASCII characters (decimal value) in the left column and the right column indicates whether the character is allowed in XML documents.

Questions:

1. Why does XML not support many of the US-ASCII characters? Of the 127 US-ASCII characters, 28 characters are not allowed in XML documents; that is, 22% of the US-ASCII characters are not supported by XML.

2. I am creating an XML Schema for an RFC that allows all 127 US-ASCII characters. What should I do for the 28 US-ASCII characters that are supported by the RFC but not supported by XML?
 

Decimal value of
US-ASCII character | Is an XML character?
------------------------------------------
    1              |  No
    2              |  No
    3              |  No
    4              |  No
    5              |  No
    6              |  No
    7              |  No
    8              |  No
    9              |  Yes
   10             |  Yes
   11             |  No
   12             |  No
   13             |  Yes
   14             |  No
   15             |  No
   16             |  No
   17             |  No
   18             |  No
   19             |  No
   20             |  No
   21             |  No
   22             |  No
   23             |  No
   24             |  No
   25             |  No
   26             |  No
   27             |  No
   28             |  No
   29             |  No
   30             |  No
   31             |  No
   32-127    |  Yes