Summary: cream is higher in fat than evaporated milk. Molasses has a strong flavor.
Without the amounts or the techniques, it’s difficult to tell, but there are definitely differences in these two recipes for caramel coating.
Karo is a brand of syrup. White Karo is their light corn syrup.
Brown sugar is sugar with molasses. Nowadays, it is usually white sugar with molasses added back in, but it can be sugar before the molasses is removed depending on the brand.
If you replace the ingredients with what they are, you have:
- light corn syrup
- evaporated milk
- evaporated milk
- whipping cream
Evaporated milk and cream are often used interchangeably, especially in older recipes; however, cream has a much higher fat content than evaporated milk. Evaporated milk has no less than 6.5% milkfat, where whipping cream has no less than 30-36% milk fat, depending on whether you use light or heavy whipping cream. (From the International Dairy Foods Association; also, more detailed requirements from the United States Code of Federal Regulations.)
That is, whipping cream has about five times more fat than evaporated milk. So, depending on the amounts (including the amount of butter, which is almost all fat) and the techniques (how hot you cook each syrup, for example, will have a major effect), your caramel coating for apples has much more fat in it than your candy coating for corn. I would expect your candy apples to be crunchier than your caramel corn although this will heavily depend on technique.
Corn syrup is often used to decrease the chance of crystallization, which may make your candy apple recipe easier than your caramel corn recipe but that will depend a lot on the techniques and the amounts.
The caramel for your apples may also stay dippable longer than the caramel for your popcorn would, due to the syrup, but the amount of fat in the caramel corn recipe may offset this.
Molasses will also impart a different flavor to your popcorn that your candy apples do not have. I would expect the caramel for your popcorn to add a more robust flavor.
Depending on how (or whether) you caramelize the caramel in either recipe, the caramel for your popcorn is meant to add to the flavor of your popcorn. The caramel for your apples is meant to enhance the sweetness of the apples.
Popcorn is naturally less sweet than apples. Popcorn is less than 1% sugar, whereas apples run from about 11% to 13% sugar for common varieties, and probably more for especially sweet varieties.