strange query plans, won't use index

Does anybody know where there is a difference here:

photo=> explain select cat from wwwacl where userid=getwwwuser('dustin');
NOTICE: QUERY PLAN:

Seq Scan on wwwacl (cost=2.65 size=5 width=4)

EXPLAIN
photo=> explain select cat from wwwacl where userid=6;
NOTICE: QUERY PLAN:

Index Scan using acl_byid on wwwacl (cost=2.24 size=5 width=4)

EXPLAIN

getwwwuser('dustin') returns 6 here.

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SA, beyond.com My girlfriend asked me which one I like better.
pub 1024/3CAE01D5 1994/11/03 Dustin Sallings <dustin(at)spy(dot)net>
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