The catch is that you're looking at this through the lens of "comparison shopping between two user-facing apps", decided on by a random consumer out on the net. In that context, it's absolutely true. I personally experienced this with google vs. all of the other portal search sites like yahoo, excite, etc - google loaded much faster, and on my shitty 28.8 modem that was a matter of minutes, sometimes. So I switched to google.
The thing is - most web software isn't comparison shopped. It's developed on contract. I work at a company that does a lot of this, and, hypothetically, maybe we'd get hired to do an internal app for some retailer (imagine Best Buy or Walmart). When you build something like that, there's a gun to your head about time-to-deliver. They don't care if it's good — it's just got to meet a "reasonably decent" metric of quality. The only thing they really care about is getting it released on a certain timetable.
And all of this is because of contract law - timetables are provable breach-of-contract. You promised you'd make something by February, but you weren't done until April - that's something that's a provable failure-to-deliver. That's got financial penalties. But quality? Quality's gotta be astoundingly bad to be "provable". "Lag" or "the site's kinda slow" doesn't hold up in a lawsuit. (These things rarely lead to lawsuits, but do lead to 'punishment' by a refusal to renew a contract, knowing that the contractor can't sue the company because the contractor provably failed to deliver what was agreed on.) So they optimize for what's punishable according to the terms of the contract.
That's why all of this corporate enterprise software sucks - because nobody gets punished if it's slow or crappy; they just get punished if it's late, or if it's provably broken, because that's the stuff that's easy to pull out of a contract for.