Is this really a surprise to anyone?
The (seemingly) low boost in hardware sales compared to the number of Grand Theft Auto 4 software units sold last week should have been a sign that GTA4 was potentially as front loaded as Halo 3; this means that it could take 6 (or more) months for the first week sales to account for less than 50% of total number of units sold. When you factor in (potential) used software sales from such a massive title, it may even take longer (or might not happen at all) ...