Not neccessarily. PCI-E is capable of more bandwidth, but there's still plenty of bandwidth left in AGP. The industry, however, chose to move to PCI-E, so everyone moved.
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AMD X2 3600+@3.00|2GB Crucial Ballistix Tracer PC2-8500|evga 7900 gs (750/1780) Volt-moded|ASUS M2N32-SLI Deluxe|2 x NEC Multisync 90GX2 19"