Sure, but Excel is presumably one of the most optimized (in terms of the amount of money and brainpower devoted to optimizing it) applications in existence.
That's the price of backward compatibility. But I think it's a bit of a "Seinfeld is unfunny"[1] situation; if Microsoft decided to save on the nine-figure budget and outsource Excel development to, say, your favorite purveyor of antivirus software, you'd notice real fast.