Yeah but the guy said explicitly that he was comparing the two providers. It's like me walking into a Ford dealership and saying that I'm trying to decide between a Taurus and a Chevy Malibu.
Direct comparisons would be reasonable and helpful although you'd be a fool not to vet them afterwards. If a competitor is missing a feature (24x7 support in this case), I'd say that's absolutely fair game.
Even if you want to be very direct about your competitive differences, you can do it without ever stating an overt negative. Just say, "ask them if they can XXX", or "ask them if they really YYY". Then say "we can, and here's why that's awesome:".
One very simple reason why the direct comparison is a bad idea is right there in the blog post: Heroku falsified one of the Engine Yard guy's claims, and blew his credibility up. There's always a risk that can happen to you when you badmouth a competitor.
Be subtle about competitor flaws, and very very overt about your benefits.
Direct comparisons would be reasonable and helpful although you'd be a fool not to vet them afterwards. If a competitor is missing a feature (24x7 support in this case), I'd say that's absolutely fair game.