The reason:

Posted Jun 14, 2012 12:25 UTC (Thu) by cortana (subscriber, #24596)
In reply to: The reason: by przemoc
Parent article: Quotes of the week

AFAIK packages in non-free are not auto-built by default. So a lack of an officially-build amd64 instance of this package probably just means that the maintainer didn't go through the steps to request that it by autobuilt.

On the other hand, now that multiarch is present in testing/unstable:

$ dpkg-architecture -qDEB_HOST_ARCH
amd64

# apt-get install lgrind
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Recommended packages:
  tetex-bin:i386
The following NEW packages will be installed:
  lgrind:i386
0 upgraded, 1 newly installed, 0 to remove and 1 not upgraded.
Need to get 81.8 kB of archives.
After this operation, 250 kB of additional disk space will be used.
Get:1 http://ftp.uk.debian.org/debian/ wheezy/non-free lgrind i386 3.67-3 [81.8 kB]
Fetched 81.8 kB in 0s (303 kB/s)
Selecting previously unselected package lgrind.
(Reading database ... 447986 files and directories currently installed.)
Unpacking lgrind (from .../lgrind_3.67-3_i386.deb) ...
Processing triggers for man-db ...
Processing triggers for doc-base ...
Processing 1 added doc-base file...
Registering documents with scrollkeeper...
Setting up lgrind (3.67-3) ...
texhash: Updating /usr/local/share/texmf/ls-R... 
texhash: Updating /var/lib/texmf/ls-R-TEXLIVEMAIN... 
texhash: Updating /var/lib/texmf/ls-R-TEXLIVEDIST... 
texhash: Updating /var/lib/texmf/ls-R-TEXMFMAIN... 
texhash: Updating /var/lib/texmf/ls-R... 
texhash: Done.
W: Operation was interrupted before it could finish

$ ldd /usr/bin/lgrind
	linux-gate.so.1 =>  (0xf77d4000)
	libc.so.6 => /lib/i386-linux-gnu/i686/cmov/libc.so.6 (0xf764d000)
	/lib/ld-linux.so.2 (0xf77d5000)

Not too impressive since I already had libc6:i386 installed, and lgrind has no other dependencies, but you can see how multiarch nicely makes obsolete the old biarch problems that jschrod lists in a post above.