  The CDF 3.7 sigma evidence of pure annihilation $B_s \to \pi^+ \pi^-$ decays,
if confirmed, would imply a large annihilation scenario in the QCD
factorization approach. This is somewhat unexpected as the large annihilation
scenario was disfavored in previous studies. In this paper we reinvestigate the
role of annihilation topology in QCD factorization. We find that it is not easy
to reach the CDF central value of $B_s \to \pi^+ \pi^-$ decays when other decay
channels are considered. Our analysis also reveals that, for well-measured
charmless B decays into two final pseudoscalar mesons, the QCD factorization
predictions with large annihilation parameters show good agreement with the
experimental data except $B_s \to K^+ K^-$ and $B_d \to K^0 \bar{K}^0$ decays.
Though other possibilities can not be excluded, this may indicate that the
SU(3) flavor symmetry breaking should be taken into account for the
annihilation topology. In addition, there are different annihilation
topologies, so that somewhat different annihilation parameters may be chosen
for different final states and different annihilation topologies. If so, the
predictive power of the QCD factorization method may be rather limited for many
decay channels.
