I expect some of the demand is due to the fact that JetBrains releases new major versions of their products 2 or more times a year (ReSharper for example), and conveniently bundle important bug fixes into those versions instead of fixing the bugs in previous releases.
So anyone who's - for example - still using ReSharper 6 will probably leap at this opportunity to finally get fixes for critical bugs in the product. Normally you'd have to pay $100 or more to upgrade just for bug fixes; now it's a rather more reasonable $30 or so.
"More reasonable" points exactly to what I'm talking about.
If the demand for this offer is so intense their servers melt down for hours on end it seems this is pointing to a huge opportunity the rest of the year to reach all those who think 4x the current sales price (whether for the full version or the update) is "unreasonable".
One data point would be myself: as a single developer, spending 100€ on AppCode never felt "reasonable" considering XCode was free. 25€ is an instabuy of course - so it seems to me the "sweet spot" is more around 50-60€ where they'd reach far more than twice as many customers than at 100€...
It's easy to assume that a sale price is a better year-round price, but it doesn't always work that way. Yes, there's pent up demand for the 75% off price, but the people who are buying it are the people who didn't want to buy it at full price. JetBrains has been in business for a while and must have clearly sold a LOT of licenses at full price for them to be releasing new products/versions.
Flash sales like this are used to maximum revenue. They earn full price most of the year and do flash sales to get everyone that doesn't want to pay full price to pay something.
Coupons work the same way. If your price sensitive you'll spend the time to clip coupons and get the better deal. If you're less price sensitive, you won't "waste your time" with coupons and will pay full time. Sales and profits increase for the company.
It's not just people that didn't want to buy at full price. It's also people that would have purchased at full price eventually being compelled to act today by the huge discount.
For example I bought AppCode and PyCharm today instead of waiting until Q1 of next year like I originally planned.
Once you get past the initial purchase, upgrades cost 59, which is right in the sweet spot you mentioned. I'm guessing this is not an accident.
There are definitely a good number of people that might not consider the full price worth it, but that's why JetBrains has occasional sales around holidays, back to school, etc.
So anyone who's - for example - still using ReSharper 6 will probably leap at this opportunity to finally get fixes for critical bugs in the product. Normally you'd have to pay $100 or more to upgrade just for bug fixes; now it's a rather more reasonable $30 or so.