That would imply that debt-servicing is their dominant cost. That seems wrong (e.g., a grocery store presumably spends a large fraction of its revenue on purchasing groceries from wholesalers).
That'll spill over into losses for the financial sector, possibly a CMBS meltdown and a financial crisis, which will spill over into the real economy.
All the job losses in housing and real estate and the hit to the financial sector will result in unemployed people who are no longer buying stuff so you'll see a contraction in everything consumption related. That'll lead to much lower ad buys, so that'll hit the ad companies. They'll all layoff staff which acts as a positive feedback loop.
Right now mostly we're just seeing companies whose CEOs see this coming down the pike who are laying off some staff early and trying to position better for the recession.
It isn't correct to say that e.g. Google's business is reliant on them flipping over loans cheaply, but they are certainly dependent upon other businesses in the economy being able to flip over loans cheaply.
If a grocery store makes 1% profit on each item it sells, and its debt service cost is 1% of its revenue (making it roughly "1% of its cost") a doubling of debt service cost wipes their margin to zero.
Say you make $100 in revenue and $1 in profit, and $1 of your $99 in costs is debt service. Your debt service increases to $2, your profit drops to zero.
Now your revenue increases to $101, presumably your debt costs stay fixed (this is not a guarantee - revenue expansion costs money), but your non-debt-service costs scale as well, and they are now 0.98 * $101 + $2 in debt service = $101.98. Congratulations, your profits are positive again, but they are $0.02.
I am eliding here the general difference between fixed costs and variable costs, and so it's probably not true that your costs would scale quite this much with revenue, but it's much closer to the truth than that you'd be back where you started, esp. in a low margin business.
Bear in mind HN's view of the business world and profit margins and expenses is heavily skewed by the industry we work in, which remains one of the most profitable in the world across a wide variety of subsectors. The profit margin an incredibly profitable grocery or shipping company might have would be considered a danger flag for a tech company, and I don't just mean the big ones, either. A profit margin of 5% is not uncommon and 10% is doing extremely well for most businesses. It's easy to look at numbers in the millions or billions and think they can take anything because in absolute terms on a single human's scale they've got more money than you can imagine, but it doesn't necessarily take very much by percentage points before the profits of a normal company go "poof".
Based on your thoughts here I'm going to assume you haven't worked at a small business before. If you have it must have been awesome to work at a place that didn't have to borrow money constantly.