In ELIC all the characters mention how much they love each other very frequently. However, there is never a notable demonstration of love between two characters, nor do they really act in any way to prove that they love each other. This gives the phrase a sort of hollowness, where it is repeated too often to be taken seriously and ends up not being believed. Whether or not Foer meant for this to happen seems uncertain, but there is an impression of him trying to create ties between his characters with the words "I love you", and the resulting ties ending up weak and half-formed.
I think Foer purposely created weak ties between the characters to show how the modern-day world seems broken and hollow. This sense of being "broken" is highlighted by how dysfunctional Oskar's family is after his father's death. The family members often proclaim their love because they are unable to express it in any other way. All of them need love, but are in someway "broken" by past experiences and have a hard time expressing it (a possible exception is Oskar's mom). Another thought: if the world seems hollow, how can people form relationships that are "full"?
"'I love that,' I told her, and not just because I wanted her to like me. 'You love what?' she asked. I pointed at the picture. 'Thank you,' she said. 'I like it, too.' I said I loved it.' 'Yes. I love it.'" pg. 94
" "Do? You? Really? Love? New York?" He said, "New York?" I said, "Your. Shirt." He looked at his shirt. I pointed at the N and said "New," and the Y and said "York." He looked confused, or embarrassed, or surprised, or maybe even mad. I couldn't tell what he was feeling, because I couldn't speak the language of his feelings. "I not know was New York. In Chinese, ny means 'you.' Thought was 'I love you.' " (239)
I think sometimes people have troubles actually showing their emotions with love, even if they speak it.
"I'd never loved Grandma more than I loved her right then."