18 Pa.C.S. § 6109 (Licenses)
is the applicable statute. Section (e)(4) was added via act 66, 2005 (2005-66) and was slated to take effect "upon publication of the notice under 18 Pa.C.S.A. § 6109(h)(2) or five years and 60 days [Jan. 10, 2011], whichever is first."
The text of (e)(4) is as follows:
The sheriff shall require a photograph of the licensee on the license. The photograph shall be in a form compatible with the Commonwealth Photo Imaging Network.
This is the part that caused the counties to require in-person application, since they had (and have) not figured out how to satisfy the second sentence of that section aside from using their own image capture system. From the Centre County website
License to Carry Firearms Applications Via Mail Discontinued as of March 31, 2011
As the result of requirements of Act 66, 2005, applicants must have their photo and signature captured electronically into our system. At this time there is no manner to complete these requirements without the personal appearance of the applicant.
Therefore we will not be able to process any mailed applications received after March 31, 2011.
For some reason that I can not determine, (e)(4) did not take effect until March 31st, 2011. I seem to remember some counties protesting the change, maybe the state gave them an extra couple of months to comply.
So, again, there is no law prohibiting both application and issuance of an LTCF by mail, but they have not established a way to comply with §6109 (e)(4) that doesn't involve in-person appearance. Many counties will have no problem mailing the license to you once you have applied in person.