Lacerte, which is basically the desktop version of ProConnect, has basically no limit - I had 50 countries on one return last year.

The IRS *really* wants the countries separated, because people are claiming the full amount of withholding as creditable, even when a lower treaty rate applies. Reporting by country lets the IRS know that you're only getting credit for the actual tax liability. There has been a ton of IRS-sponsored CPE last year and this year, trying to get the word out.