Pogba was always going to get sold.
With De Gea it's different.
Real love their shiny new toys, particularly right after they've lit up international tournaments. Add to that the fact he's a Spaniard, and he'd become even more desirable.
But Spanish players in the PL tend not to get a lot of coverage in their home country. Euro 2016 was De Gea's chance to sell himself to the Spanish public. Don't forget that quite a lot of them wanted Casillas to be first choice. They simply don't rate DDG as highly as we do because they don't watch him very often. Luckily, he did nothing to change their opinions over the Summer. If he'd be amazing, every single Madridista would have been clamouring for his signature.
United's signings are nowhere near as political as Real's. You can't compare.