I can't argue against the fact that you may get more "bang per buck" with 32-Bit only systems, but you have to realise how much "bang" you need, and current 32-Bit only systems (AMD Sempron, Low end Pentium 4/Celerons) do not offer enough to run even the most demanding 32-Bit applications, never mind 64-Bit ones.
If you need high performance 32-Bit processing, then it's a truth that the fastest (and even the mid-range) processors in this field happen to be 64-Bit as well. The exception to this would appear to be the Pentium-M systems, which are a niche market and come at a steep premium, even on the desktop motherboards (which are practically non-existant).
Any system is going to be obsolete soon after you buy it. If all you need is casual web browsing, word processing and office tasks like such, then a 32-bit only processor is going to be fine. But these processors are almost obsolete already. 64-Bit processors offer the best of both sides, with high performance 32-bit processing now, and even if you buy a "bottom of the range" 64-Bit processor, at least some ability to prolong your investment as 64-Bit becomes more mainstream.