surprising behavior: `wildcard' expands tilde, but `shell' doesn't

[Eric Hanchrow]

all:
        @echo wildcard: $(wildcard ~)
        @echo shell   : $(shell echo ~)

# GNU Make version 3.78.1     (as shipped with RedHat 6.2)
# GNU bash, version 1.14.7(1) (as shipped with RedHat 6.2)

# Here's the output I get:

# 09:00:28 [erich@emerald erich]$ make -f weird 
# wildcard: /home/erich
# shell : ~

# I would have expected *both* commands to have expanded the tilde,
# not just the command that calls `wildcard'.