They are not the same.

http://www.degussa-foodingredients.de/foodingredients/html/e/health/eng/kh/l6.1.htm

http://www.biochem.arizona.edu/classes/bioc801/tutorial/Lec34T.ppt

http://www.herbalgram.org/iherb/expandedcommissione/he090.asp

"Description
Soy lecithin consists of the phospholipids extracted from the seeds of Glycine
max (L.) Merrill [Fam. Fabaceae] and its preparations in effective dosage. Soy
lecithin contains (3-sn-phosphatidyl)choline, phosphatidylethanolamine, and
phosphatidylinositol.

Chemistry and Pharmacology
The main constituents are a natural mixture of phosphatides, mainly
phosphatidylcholine (20-31.6%), phosphatidylethanolamine and
phosphatidylinositol, in combination with fatty acids, carbohydrates, and other
substances (DAB, 1998; Der Marderosian, 1999; Der Marderosian et al., 1988; FCC
III, 1981; CFR 21, 1998). Soybean lecithin contains 11.7% palmitic, 4% stearic,
8.6% palmitoleic, 9.8% oleic, 55.0% linoleic, 4.0% linolenic, and 5.5% C20 to
C22 acids (Budavari, 1996; Der Marderosian, 1999). Pharmacopeial grade soy
lecithin must contain a minimum 20% and maximum 31.6% phosphatidyl choline,
calculated on the dried substance. Its iodine number value must be between 76
and 85, its acid value maximum 35, and peroxide value maximum 10 (DAB, 1998)."

http://www.whatislife.com/reader2/Metabolism/pathway/phospholipid.html

"1,2-diglyceride is a precursor for both phosphatidylcholine (C00157, lecithin)
and phosphatidylethanolamine (C00350) by combining the diacylglycerol with an
activated choline (ethanolamine) group using the nucleoside CTP to form
CDP-choline (C00307) and CDP-ethanolamine (C00570), respectively. Choline is
activated by phosphorylation using ATP to phosphorylcholine and
phosphorylcholine in turn is formed to CDP-choline by CTP releasing
pyrophosphate as byproduct.

These committed reactions are analogous to the activation of glucose-1-P to
UDP-glucose for glycogen synthesis. Phosphatidylethanolamine can also serve as
precursor for phosphatidylcholine by transfer of three activated choline groups
In addition, phosphatidylserine is derived from phosphatidylethanolamine by
exchanging the ethanolamine headgroup for serine.

Two minor phospholipids are phosphatidylglycerol (PG) and (PI). They are derived
from phosphatidic acid instead of 1,2-diglyceride. Phosphatidic acid is
activated by activation using CTP to form the high energy compound
CDP-diglyceride (C00269). The cytosine unit is replaced by either inositol to
form phosphatidylinositol (PI) and CMP, or glycerol-3-phosphate to form
phosphatidylglycerol (PG) and CMP and Pi. Both PG and PI are negatively charged
phospholipids because of the single negative charge contributed by the phosphate
ester linkage."

So it is clear that phosphatidylinositol is a *specific form* of  lecithin. The
point is whether a mixture of phospholipids would have the same the same effect
on cholesterol as phosphatidylinositol or not.