HP/Level - Huge disparity between Glyphs and Seals.

So I was making Pages for AD Mids - one to deal with Magic Damage threats (Armor Pen Marks, Armor Pen Quints, HP/Level Seals, MR/Level Glyphs), and one to deal with Physical Damage threats (Armor Pen Marks, Armor Pen Quints, Armor/Level Seals, HP/Level Glyphs).

But then I realized that there's a HUGE disparity between the quantity of HP/Level you get.

9x HP/Level Seals @ Level 18: 216 9x HP/Level Glyphs @ Level 18: 88

...a 128 HP difference. And this confuses me because I always thought the only difference between Defensive Stat Glyphs and Defensive Stat Seals was what type of damage it was dealing with. Since HP is damage type-neutral (i.e. it's equally effective against both Magic and Physical Damage), I see no reason that HP/Level Glyphs should provide as much as Seals - or an average of the two (i.e. Glyph HP/Level + Seal HP/Level divided by 2) so that people wouldn't abuse it and take both HP/Level Glyphs and HP/Level Seals.