Hi supreme.
Guitar servicing is just one example of a service. As with what CyanideJunkie mentioned, we usually visit a private clinic/polyclinic to see a doctor. For this scenario, it's the total opposite where you're requesting the doctor to come to your place. Well, with top dollar, definitely such a service would exist. However, if you think from the guitar servicing service provider perspective, it's not exactly a lucrative business considering the time and effort for travelling and the uncertainty of time taken for each 'job'.