Are DSA2 signing keys backwards compatible?

[Kevin Hilton]

>You could use SHA-512 with
>it if you liked, but the hash would be truncated to 256 bits.

Interesting.  Are the higher or lower bits truncated?

>We follow the advice in FIPS 180-3:
>
>      L = 1024, N = 160
>      L = 2048, N = 224
>      L = 3072, N = 256

Ok.  So back to the ever asking defaults question, so why when I
produce a 3072 bit DSA signing key, why isnt my first digest hash
preference or choice SHA-256?  Here is what I am getting:

pub  3072D/0053175A  created: 2007-11-14  expires: never       usage: SC
                     trust: unknown       validity: unknown
sub  4096g/51BFA0E0  created: 2007-11-14  expires: never       usage: E
[ unknown] (1). -----------------------------------------------------

Command> showpref
[ unknown] (1). -----------------------------------------------------
     Cipher: AES256, AES192, AES, CAST5, 3DES
     Digest: SHA1, SHA256, RIPEMD160
     Compression: ZLIB, BZIP2, ZIP, Uncompressed
     Features: MDC, Keyserver no-modify

It would seem in fact that my digest preferences should only be SHA256
or SHA512 based on the information provided!  SHA1 or RIPEMD160
shouldn't even be listed here, correct?