Well actually, I would say the "feel" is most important. I mean if the 4e classes really aren't homogeneous, well then a Ranger in play has got to feel totally different from a Rogue, right? Otherwise for me too be able to switch out a Rogue with a Ranger and feel no real noticeable difference in feel... well that means they pretty much fell the same to play... so witch one is it?
Ok. You want each class to feel different when you play them. You postulated a hypothetical somebody who wants to play a rogue with a short bow, implying that it was hard to impossible to do, yet it's a common archetype.
Now here's the problem, I'm not the DM of this hypothetical person. No one on the thread is. (Though if someone's been in this situation, it'd be nice to hear from them.) So, I'm stuck, so to speak with a fact pattern in a hypothetical where, in order to answer it with any kind of specificity, more information would be very helpful. I can't ask a hypothetical person for answers. So here it is, this is how, in real life I would help a player who came to me and asked "how can I play a rogue who is competent in a short bow?"
First question: "how often do you want to use the bow?"
Technically, any PC of any class in every edition I've ever played can use any weapon he or she picks up. It's just that there are typically penalties. In 4e, the penalty is that the PC doesn't get the proficiency bonus. If the player just wants to use one once in a blue moon, then just buying one and keeping it for back-up might be the best option. If the player wants to get the proficiency bonus those few time he or she uses it, then I suggest the feat. Problem solved.
What if the answer is frequently?
Things get tricky. Next question.
Second question: "what do you like about the rogue class, the ability to pick pockets, disable traps, and sneak around, or do you want the benefits of things like sneak attack?"
If the player wants the pick pockets and be stealthy, then a ranger + thievery skill might work well. Another option might be to go half-elf rogue and pick up a power from another class that works well with the short bow (if the answer isn't so much frequently as often). There is also multiclassing from rogue into a class that give the rogue a power from another class that's useful with short bows. Also, the player can play a straight-up rogue elf, elfs get proficiently with short bows, then use multi-classing to gain powers useful with short bows.
Each option gives the a different feel. The ranger option gives the player thieving skills (assuming the appropriate feat or background was chosen) while a lot of powers that are very useful for someone who wishes to use the short bow almost exclusively. This creates a ranger who uses ranged weapons and can scout a head for traps and pick peoples pockets while in town.
The various rogue options keep the PC in the fight with sneak attack. Rather than using say, twin strike, to deal damage with a short bow, this option allows the rogue to get up close and deal sneak attack damage. The short bow comes in handy when the situation calls for ranged shots or when up, close combat isn't an option.
Both options create different roleplaying characteristics. Is the PC a skilled archer who need thievery to survive as an orphan? Or is the PC a skilled trickster who used archery to hunt for food in the wild? Or maybe the PC is an elf who wishes honor his god by making good use of natural archery talent? (Even though his god may not look favorably upon stealing or sneaking.)
Third question: "where do you see your character in 5 levels?"
There are tons of answers to this question, but if the answer is complicated, with lots a possibilities for short bow, thieving, and sneak attack damage then I might sugest what I think of as the 3e option (because I saw this
a lot in 3e): hybrid. Rangers and rogues are both strikers. One does so up close in melee combat, relying on classes like defenders to keep the monster occupied, while the other class relies on multiple attacks to do damage on a regular basis. By combining them, I should get a striker that can do both. Here the PC gets lots of ranged short bow powers, the skills necessary to pull off sneaky, and sneak attack damage. Such a hybrid should give the PC a different feel than either class alone, but without sacrificing effectiveness in combat.
I found ranger/rogue hybrids to be fairly common in my 3.x days, so I don't see anything wrong with it. I think those archetypes necessarily produce classes that work well together.
So my question to you is: what do you want do?