The reigning world champion was penalised for not leaving Alonso enough room on the exit of the Curva Grande on lap 26 in an incident reminiscent of when the pair battled 12 months ago.
Speaking about whether he felt it was right to be given a penalty, Vettel said: "From my point of view no, but it is not for me to judge."
When asked by AUTOSPORT for his feelings on what happened, Horner said: "It is irrelevant effectively after the DNF, but judge it for yourself - it seemed a bit harsh. It didn't seem to warrant a penalty but that is my opinion."
Vettel's sanctioning this year, compared to Alonso not being penalised in 2011, is the result of a clamp down on defensive driving issued by the FIA - as revealed by AUTOSPORT earlier this year.
In a note sent to all drivers ahead of the British Grand Prix, Formula 1 race director Charlie Whiting had clarified that: "any driver defending his position on a straight and before any braking area may use the full width of the track during his first move provided no significant portion of the car attempting to pass is alongside his. Whilst defending in this way the driver may not leave the track without justifiable reason."
To further clarify the situation he later added: "For the avoidance of doubt, if any part of the front wing of the car attempting to pass is alongside the rear wheel of the car in front this will be deemed to be a 'significant portion'."
Alonso said about the matter and how it compared to last year: "Last year it was not penalised, this year it has been. I think there is a big difference for the people who understand this movement."