It is, but in most cases (including these) the problem lies in the infrastraucture, which is not so reliable around Stockholm. The train tracks are heavily used and maintenance is always behind, and there is really no alternative routes if anything goes wrong, such as signal problems, power outages, derailements) in the narrow corridor though the city.
Isn't this exactly the reason behind the construction of Arlandabanan/Arlanda Express? Private investors figured that customers would value the reliability of dedicated tracks Sthlm C - Arlanda, hence paying the rather high ticket prices.