Wyverns, flying, and multiple attacks [BADD, help me!]

[Nareau]

Below are the stats for a wyvern. Note the following:

A wyvern can slash with its claws only when making a flyby attack, and it cannot make bite, sting, or wing attacks.

Does this mean it can attack with both claws as its flyby attack? Is this supposed to be an exception to the normal rule (you can normally only make a single attack during a round in which you move)?
It seems that the classic maneuver of the wyvern is to fly overhead, grab its prey, and fly off with it (while stinging it to death). But according to the rules, it appears that the wyvern can never do this: it can only attack with its claws while it's flying, and it can only grab you if it hits with both claws. But since it should only be able to attack you once while flying, it can't ever hit you with both claws.
This is a problem I have with lots of flying critters. If they have maneuverability of Average or worse (and they can't Hover), they can't ever make multiple attacks while airborne. Are there lots of exceptions for this rule? Am I misinterpreting the rules? Can you propose a good solution?
As always, please cite sources if you can. Thanks.

Wyvern

Huge Dragon
Hit Dice: 7d12+14 (59 hp)
Initiative: +1 (Dex)
Speed: 20 ft., fly 60 ft. (poor)
AC: 17 (-2 size, +1 Dex, +8 natural)
Attacks: Sting +9 melee, bite +4 melee, 2 wings +4 melee; or _2 claws +9 melee
Damage: Sting 1d6+4 and poison, bite 2d8+2, wing 1d8+2; or claw 1d6+4
Face/Reach: 10 ft. by 20 ft./10 ft.
Special Attacks: Poison, improved grab, snatch
Special Qualities: Scent
Saves: Fort +7, Ref +6, Will +6
Abilities: Str 19, Dex 12, Con 15, Int_6, Wis 12, Cha 9
Skills: Listen +13, Move Silently +9, Spot +13*
Feats: Alertness, Flyby Attack

Climate/Terrain: Temperate and warm forest, hill, and mountains
Organization: Solitary, pair, or flight (3-6)
Challenge Rating: 6
Treasure: Standard
Alignment: Usually neutral
Advancement: 8-10 HD (Huge); 11-21 HD (Gargantuan)

Some wyverns speak Draconic, but most are too stupid to understand any language.

Combat

A wyvern can slash with its claws only when making a flyby attack, and it cannot make bite, sting, or wing attacks.

Poison (Ex): Sting, Fortitude save (DC 17); initial and secondary damage 2d6 temporary Constitution.

Improved Grab (Ex): To use this ability, the wyvern must hit with both claw attacks. If it gets a hold, it hangs on and stings.

Snatch: If a wyvern gets a hold on a creature four or more sizes smaller, it automatically deals damage with both claws and its sting attacks each round the hold is maintained. The wyvern can drop a creature it has snatched as a free action or use a standard action to fling it aside. A flung creature travels 30 feet and takes 3d6 points of damage. If the wyvern flings it while flying, the creature suffers this amount or falling damage, whichever is greater.

Skills: *Wyverns receive a +3 racial bonus to Spot checks when flying during daylight hours.

 

[Gromm]

Seems to me its a special rule for Wyverns. Normally you could only make one attack, but Wyverns can make 2 claw attacks only as part of a flyby attack.
Creatures break the rules all the time. This one doesn't really bother me since it makes sense. I can see the Wyvern basically pouncing on a creature with both its claws and carrying it away into the sky.

 

[Dr. Zoom]

I would say to either let it flyby and get two claw attacks as an exception to the rule, or change its claw attacks to "Claw +9 melee." IOW, it gets one attack that includes both claws together. Change the damage to 2d6+4 (It can only get its strength bonus once). If you do it this way, it will be easier to make the improved grab.

 

[(Psi)SeveredHead]

It should get a damage bonus of +6, since it's a two-claw attack. Look at the troll's rend ability for proof.