For Roy this would make sense, since he's a fighter and thus has a huge number of feats. For most other characters, though, it's pretty easy to pin them to a particular number of feats, since feats advance slowly with level and non-fighters have a relatively limited selection of bonus feats.
edit:
Just to show it's possible, here's a feat analysis for Haley. She's a 16th level human rogue, so she has the following feat slots available:
H - Martial Weapon Proficiency (Longbow)
1 - Point Blank Shot
3 - Rapid Shot
6 - Dodge?
9 - Manyshot
10 (RSA) - Ranged Pin?
12 - Ranged Sunder
13 (RSA) - Precise Shot
15 - Improved Precise Shot
16 (RSA) - ???
Feats marked (RSA) are bonus feats from a Rogue Special Ability. These may be any feat, but they're relatively infrequent. The first feat Haley demonstrates she has is MWP (Longbow). In strip 62 she demonstrates both Rapid Shot and Manyshot, which also imply Point Blank Shot, so I'll give her those as early as she can take them. She then uses Ranged Pin (we assume) on Roy's corpse. There's no obvious way to do what she does in the rules, but Ranged Pin is fairly close. Next she Ranged Sunders a hobgoblin's whip. Then in #615 she says she's "got a feat that does most of [what the Seeking property would grant her]". This feat is Improved Precise Shot (ignore less than total cover/concealment; it's rare that she'd be able to target someone with full cover or concealment, so Seeking isn't a big upgrade), which requires BA +11 and Precise Shot. Thus IPS is her 15th* level feat and Precise Shot is either her 13th or 6th level feat. According to SSDT, which I don't own, she also has Dodge. To be conservative, I'll give her Dodge at level 6 and Precise Shot at level 13. It's not totally clear how much stuff carries over from SSDT, so she might not actually have that feat.
Dodge and Ranged Pin are the most questionable feats here, but they're legal and don't determine her level so I settle on the side that she does have them. She may or may not have another feat, gained from her 16th level Rogue Special Ability. If we ever see her clearly take half damage from a threat that offers a Reflex Save (I don't think we have), we'll know she spent it on Improved Evasion. There are others, but that would probably be the most obvious one, as many relate to melee combat.
* The table of levelups currently lists #648 for her 15th level. Both 648 and 615 demonstrate that she is level 15, but 615 is first, so she's got the level a bit earlier than we currently state.
e2:
Just for fun, I did a set of these tables for the entire OOTS. My table for Belkar is in a previous thread and I won't take up more space with the rest of them unless someone asks. That said, it's interesting to note that Roy has only two free feat slots left. They don't need to be fighter bonus feats, though, and they can move around pretty freely. If there's some way for him to get around the Large size requirement (without spending another feat, obviously), those last two feats could be Rock Hurling and Fling Enemy (e3: actually, it's possible his throws of Xykon and Enor could be explained by Martial Study (Mighty Throw) instead of Improved Grapple and maybe Fling Enemy). Unless someone can come up with a way for Roy to avoid the size requirement, though, I don't think those things are adequate evidence. Regardless, Belkar has one free feat slot (maybe zero if there's a way for the Bounding Assault advocates to save CDMI), depending on how the current argument resolves, Vaarsuvius has five, Elan has three, and Durkon has three.