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E, Danielbecause in both that specific article and every other I researched on the web, the suggestion is that people 'collected' them through the very process by which they were intended. That is, they were mailed to friends and family who kept the items as keepsakes for what I am sure is very many reasons, and this is what is meant by the term collecting at the time. No doubt the aesthetics and boom in sending postcards created a 'fad' interest for a number of years (referred to as the golden years of postcards) where people the world over kept and collected the items in scrapbooks and other mediums, memories of travels taken and new friends or family made, a short and filable "movie 8" of its time.
I have yet to read nary a sentence that describes people collecting postcards of the time as we understand collecting today. That is, buying the postcards themselves purely for the intent of creating a collection, based on specific areas of interest, and not for the purpose of sending greetings on beautifully rendered artworks to friends which was the primary intent and vehicle of the item.
No doubt some indeed were pure collectors (I read of a Jewish collector who amassed postcards with specific religious themes), but I would argue nearly all were postcard collectors then much as they are today, and that postcards even with sporting interests were viewed as such - and not baseball cards to be collected by children and idle men. 
Further reading also makes an interesting point regarding blank baseball postcards.
"On December 24th, 1901, the U.S. Government allowed the use of the words "Post Card" or "Postcard" to be printed on the undivided back of privately printed cards and allowed publishers to drop the authorization inscription previously required by law. Writing was still only allowed on the front of picture side of the card but right at this time, other countries began to permit the use of a divided back, allowing the front to be primarily for the picture or artwork and the back left for the address and any message. England was the first to allow divided back cards in 1902, France followed in 1904, Germany in 1905 and finally the United States in 1907. These changes brought in the "Golden Age" of postcards as millions were sold and used."
The reason I think this date interesting is that quite a number of the postcard issues in our hobby appear dated to the 1907-09 period, and may well have been prepared to take advantage of the upcoming relent on messages printed on the back of the card. Because of the timing, it seems quite possible some people simply didn't jump on the bandwagon straight away or were unaware of the new govt. tolerances and decided they couldn't pen anything of worth across these often darkened black and white baseball images we find on many period baseball themed postcards. Or maybe they just liked them too much and kept them for the memory invoked.
And those Rose Co. cards, well, they were just too damn beautiful to butcher with fountain ink! 
Again, for me this is very different to the active pursuit of sets of cards that are focus specific, finite in number per the issue, 'checklistable' at the time in some manner or other so that individual examples can be chased,
and is part of a longer (many years as opposed to a summer interest with the dashing Mathewson or Cubs immortalized in poem) penchant that is fuelled by manufacturers producing issue after issue, year after year, to sate the collector interest.
I haven't and am not interested in hiding anything in this discussion JK, I've done my share of reading on the subject and come to my own set of understandings - and am equally pleased to think on and incorporate other ideas that are shared openly and generously by others.
That's all I'd ask, but seemingly you are itching more for argument and one upmanship than real discussion that can arise from this post.
A shame as far as I see it.
Sincerely
Daniel