Nobody's saying that the Sempron combo wouldn't be better, but for around $50 (less than current Sempron deals) Syringer can get up to a 50% boost in CPU performance (stock 1GHz to 1.4GHz, 128k cache to 256k) for very little work. With a Sempron deal, gotta purchase RAM, then may have to purchase a power supply, then have to swap out many parts instead of just a CPU, then may have to reinstall Windows after it dies from the new motherboard, then have to install motherboard drivers.
I do agree that the Sempron would definately be faster, hands down and in all cases. However, there's something to be said about a cheap and easy 50% boost in performance.