Being numbered among a group means that you are part of that group.
I'm not making an appeal to popularity, if that's what you're thinking. I'm saying that Peter
Do you not remember what Jesus said?
“Assuredly, I say to you, whatever you bind on earth will be bound in heaven, and whatever you loose on earth will be loosed in heaven. - Matthew 18:18
http://www.biblegateway.com/passage/?search=Matthew18:18&version=NKJV
He was talking to His disciples.
His disciples, the Twelve (minus Judas who had killed himself, making them "eleven") decided to replace Judas. That's literally what the Bible says! JUST READ IT!
And in those days Peter stood up in the midst of the disciples (altogether the number of names was about a hundred and twenty), and said,“Men and brethren, this Scripture had to be fulfilled, which the Holy Spirit spoke before by the mouth of David concerning Judas, who became a guide to those who arrested Jesus;for he was numbered with us and obtained a part in this ministry.”(Now this man purchased a field with the wages of iniquity; and falling headlong, he burst open in the middle and all his entrails gushed out.And it became known to all those dwelling in Jerusalem; so that field is called in their own language, Akel Dama, that is, Field of Blood.)“For it is written in the Book of Psalms: ‘Let his dwelling place be desolate, And let no one live in it’; and, ‘Let another take his office.’“Therefore, of these men who have accompanied us all the time that the Lord Jesus went in and out among us,beginning from the baptism of John to that day when He was taken up from us, one of these must become a witness with us of His resurrection.”And they proposed two: Joseph called Barsabas, who was surnamed Justus, and Matthias.And they prayed and said, “You, O Lord, who know the hearts of all, show which of these two You have chosento take part in this ministry and apostleship from which Judas by transgression fell, that he might go to his own place.”And they cast their lots, and the lot fell on Matthias. And he was numbered with the eleven apostles. - Acts 1:15-26
http://www.biblegateway.com/passage/?search=Acts1:15-26&version=NKJV
Judas was replaced with Matthias, and Matthias was numbered with the eleven, just as Judas was, and he took Judas's office.
This did not happen for Paul or any of the apostles afterwards, because the TWELVE Apostles (a group, just as the nation of Israel is a corporate entity, a group with which God made a covenant) will sit on TWELVE thrones ruling the TWELVE tribes of Israel.
Neither Paul nor any other other apostle was ever "numbered with the [Twelve Apostles].
Only if Jesus did not give the Twelve the authority to decide such matters. And He did, as per Matthew 18:18. Why do you think the disciples prayed to Jesus in Acts 1:24-25 for God's will to be done in choosing who to replace Judas with? They clearly thought they had the authority to do so.
Also, if Jesus is the only one that matters in this sort of context, then why did the twelve agree with Paul, against what Jesus said, for the Twelve, including Matthias, to only go to the circumcision, and remain mostly in Jerusalem for the rest of their lives, while Paul, only ONE apostle, goes to the rest of the world?
What you say has the "eleven" directly disobeying Christ without any good reason. Do you think God would honor them, who were to keep His commands and endure to the end, by placing them as rulers over the twelve tribes of Israel, for such disobedience?
No. The only way it makes any sense for God to do that is if He had given them the authority to decide such things (as shown in Matthew 18) for themselves,
The problem is that you have to answer the above, and why Paul hardly interacted with the other "eleven" (along with Matthias) for nearly 14 years after he was chosen, if he was supposed to have been the twelfth apostle, as well as why He said that he has no position of authority over any other believer, that he's just another member, with Christ as the head, when the Twelve (whom you assume Paul is part of) will rule over the tribes of Israel.
You also have to explain why being indirectly picked, given the qualifications listed by Peter for choosing someone to fill the office Judas left empty, disqualifies Matthias from filling the role, despite Luke (the author of Acts, who was inspired by God) to describe Matthias as being "numbered with the eleven," just as Judas was.